From 34ed62461ae4970695974afb9a60ac3df0086830 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 7 Jan 2013 13:37:42 -0800 Subject: rcu: Remove restrictions on no-CBs CPUs Currently, CPU 0 is constrained to not be a no-CBs CPU, and furthermore at least one no-CBs CPU must remain online at any given time. These restrictions are problematic in some situations, such as cases where all CPUs must run a real-time workload that needs to be insulated from OS jitter and latencies due to RCU callback invocation. This commit therefore provides no-CBs CPUs a (very crude and energy-inefficient) way to start and to wait for grace periods independently of the normal RCU callback mechanisms. This approach allows any or all of the CPUs to be designated as no-CBs CPUs, and allows any proper subset of the CPUs (whether no-CBs CPUs or not) to be offlined. This commit also provides a fix for a locking bug spotted by Xie ChanglongX . Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 5b8ad827fd86..6ad0716e65dc 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -310,6 +310,8 @@ cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp) if (rcu_gp_in_progress(rsp)) return 0; /* No, a grace period is already in progress. */ + if (rcu_nocb_needs_gp(rdp)) + return 1; /* Yes, a no-CBs CPU needs one. */ if (!rdp->nxttail[RCU_NEXT_TAIL]) return 0; /* No, this is a no-CBs (or offline) CPU. */ if (*rdp->nxttail[RCU_NEXT_READY_TAIL]) @@ -1035,10 +1037,11 @@ static void init_callback_list(struct rcu_data *rdp) { int i; + if (init_nocb_callback_list(rdp)) + return; rdp->nxtlist = NULL; for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; - init_nocb_callback_list(rdp); } /* @@ -2909,7 +2912,6 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); struct rcu_node *rnp = rdp->mynode; struct rcu_state *rsp; - int ret = NOTIFY_OK; trace_rcu_utilization("Start CPU hotplug"); switch (action) { @@ -2923,10 +2925,7 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, rcu_boost_kthread_setaffinity(rnp, -1); break; case CPU_DOWN_PREPARE: - if (nocb_cpu_expendable(cpu)) - rcu_boost_kthread_setaffinity(rnp, cpu); - else - ret = NOTIFY_BAD; + rcu_boost_kthread_setaffinity(rnp, cpu); break; case CPU_DYING: case CPU_DYING_FROZEN: @@ -2950,7 +2949,7 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, break; } trace_rcu_utilization("End CPU hotplug"); - return ret; + return NOTIFY_OK; } /* @@ -3170,7 +3169,6 @@ void __init rcu_init(void) rcu_init_one(&rcu_sched_state, &rcu_sched_data); rcu_init_one(&rcu_bh_state, &rcu_bh_data); __rcu_init_preempt(); - rcu_init_nocb(); open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); /* -- cgit v1.2.3 From b5b393601dbce0bce3f0717f29e6c8d1cf0295da Mon Sep 17 00:00:00 2001 From: Jiang Fang Date: Sat, 2 Feb 2013 14:13:42 -0800 Subject: rcu: Fix spacing problem Signed-off-by: Jiang Fang Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 5b8ad827fd86..157539a975df 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -3171,7 +3171,7 @@ void __init rcu_init(void) rcu_init_one(&rcu_bh_state, &rcu_bh_data); __rcu_init_preempt(); rcu_init_nocb(); - open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); + open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); /* * We don't need protection against CPU-hotplug here because -- cgit v1.2.3 From b0f740360efec6e6471547c0548f250bc045a233 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 4 Feb 2013 12:14:24 -0800 Subject: rcu: Avoid invoking RCU core on offline CPUs Offline CPUs transition through the scheduler to the idle loop one last time before being shut down. This can result in RCU raising softirq on this CPU, which is at best useless given that the CPU's callbacks will be offloaded at CPU_DEAD time. This commit therefore avoids raising softirq on offline CPUs. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 157539a975df..b2fc234ba1b9 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2169,7 +2169,8 @@ static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) static void invoke_rcu_core(void) { - raise_softirq(RCU_SOFTIRQ); + if (cpu_online(smp_processor_id())) + raise_softirq(RCU_SOFTIRQ); } /* -- cgit v1.2.3 From 0bdf5984ad647ba5d1c09ed66a75e5bf609456ba Mon Sep 17 00:00:00 2001 From: "Srivatsa S. Bhat" Date: Fri, 8 Feb 2013 16:11:29 -0800 Subject: rcu: Remove comment referring to __stop_machine() Although it used to be that CPU_DYING notifiers executed on the outgoing CPU with interrupts disabled and with all other CPUs spinning, this is no longer the case. This commit therefore removes this obsolete comment. Signed-off-by: Srivatsa S. Bhat Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 5 ----- 1 file changed, 5 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index b2fc234ba1b9..71df6f9f5ce6 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2931,11 +2931,6 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, break; case CPU_DYING: case CPU_DYING_FROZEN: - /* - * The whole machine is "stopped" except this CPU, so we can - * touch any data without introducing corruption. We send the - * dying CPU's callbacks to an arbitrarily chosen online CPU. - */ for_each_rcu_flavor(rsp) rcu_cleanup_dying_cpu(rsp); rcu_cleanup_after_idle(cpu); -- cgit v1.2.3 From 81e59494a56cb14f559886c345c4a93fb576bbab Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 10 Mar 2013 15:44:52 -0700 Subject: rcu: Tone down debugging during boot-up and shutdown. In some situations, randomly delaying RCU grace-period initialization can cause more trouble than help. This commit therefore restricts this type of RCU self-torture to runtime, giving it a rest during boot and shutdown. Reported-by: Sasha Levin Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 71df6f9f5ce6..0e522504ae37 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1319,7 +1319,8 @@ static int rcu_gp_init(struct rcu_state *rsp) rnp->grphi, rnp->qsmask); raw_spin_unlock_irq(&rnp->lock); #ifdef CONFIG_PROVE_RCU_DELAY - if ((random32() % (rcu_num_nodes * 8)) == 0) + if ((random32() % (rcu_num_nodes * 8)) == 0 && + system_state == SYSTEM_RUNNING) schedule_timeout_uninterruptible(2); #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */ cond_resched(); -- cgit v1.2.3 From dae6e64d2bcfd4b06304ab864c7e3a4f6b5fedf4 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 10 Feb 2013 20:48:58 -0800 Subject: rcu: Introduce proper blocking to no-CBs kthreads GP waits Currently, the no-CBs kthreads do repeated timed waits for grace periods to elapse. This is crude and energy inefficient, so this commit allows no-CBs kthreads to specify exactly which grace period they are waiting for and also allows them to block for the entire duration until the desired grace period completes. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 6 ++- kernel/rcutree.h | 12 ++++- kernel/rcutree_plugin.h | 129 +++++++++++++++++++++++++++++++++++++++++------- 3 files changed, 127 insertions(+), 20 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 6ad0716e65dc..433f426c848f 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -310,7 +310,7 @@ cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp) if (rcu_gp_in_progress(rsp)) return 0; /* No, a grace period is already in progress. */ - if (rcu_nocb_needs_gp(rdp)) + if (rcu_nocb_needs_gp(rsp)) return 1; /* Yes, a no-CBs CPU needs one. */ if (!rdp->nxttail[RCU_NEXT_TAIL]) return 0; /* No, this is a no-CBs (or offline) CPU. */ @@ -1364,6 +1364,7 @@ int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in) static void rcu_gp_cleanup(struct rcu_state *rsp) { unsigned long gp_duration; + int nocb = 0; struct rcu_data *rdp; struct rcu_node *rnp = rcu_get_root(rsp); @@ -1394,11 +1395,13 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) rcu_for_each_node_breadth_first(rsp, rnp) { raw_spin_lock_irq(&rnp->lock); rnp->completed = rsp->gpnum; + nocb += rcu_nocb_gp_cleanup(rsp, rnp); raw_spin_unlock_irq(&rnp->lock); cond_resched(); } rnp = rcu_get_root(rsp); raw_spin_lock_irq(&rnp->lock); + rcu_nocb_gp_set(rnp, nocb); rsp->completed = rsp->gpnum; /* Declare grace period done. */ trace_rcu_grace_period(rsp->name, rsp->completed, "end"); @@ -3084,6 +3087,7 @@ static void __init rcu_init_one(struct rcu_state *rsp, } rnp->level = i; INIT_LIST_HEAD(&rnp->blkd_tasks); + rcu_init_one_nocb(rnp); } } diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 7af39f4aaac4..e51373c0b748 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -196,6 +196,12 @@ struct rcu_node { /* Refused to boost: not sure why, though. */ /* This can happen due to race conditions. */ #endif /* #ifdef CONFIG_RCU_BOOST */ +#ifdef CONFIG_RCU_NOCB_CPU + wait_queue_head_t nocb_gp_wq[2]; + /* Place for rcu_nocb_kthread() to wait GP. */ + int n_nocb_gp_requests[2]; + /* Counts of upcoming no-CB GP requests. */ +#endif /* #ifdef CONFIG_RCU_NOCB_CPU */ raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp; } ____cacheline_internodealigned_in_smp; @@ -326,7 +332,6 @@ struct rcu_data { int nocb_p_count_lazy; /* (approximate). */ wait_queue_head_t nocb_wq; /* For nocb kthreads to sleep on. */ struct task_struct *nocb_kthread; - bool nocb_needs_gp; #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ int cpu; @@ -524,7 +529,10 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu); static void print_cpu_stall_info_end(void); static void zero_cpu_stall_ticks(struct rcu_data *rdp); static void increment_cpu_stall_ticks(void); -static int rcu_nocb_needs_gp(struct rcu_data *rdp); +static int rcu_nocb_needs_gp(struct rcu_state *rsp); +static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq); +static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp); +static void rcu_init_one_nocb(struct rcu_node *rnp); static bool is_nocb_cpu(int cpu); static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, bool lazy); diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 3e33aefce0ea..90a191452550 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2176,11 +2176,51 @@ static int __init parse_rcu_nocb_poll(char *arg) early_param("rcu_nocb_poll", parse_rcu_nocb_poll); /* - * Does this CPU needs a grace period due to offloaded callbacks? + * Do any no-CBs CPUs need another grace period? + * + * Interrupts must be disabled. If the caller does not hold the root + * rnp_node structure's ->lock, the results are advisory only. + */ +static int rcu_nocb_needs_gp(struct rcu_state *rsp) +{ + struct rcu_node *rnp = rcu_get_root(rsp); + + return rnp->n_nocb_gp_requests[(ACCESS_ONCE(rnp->completed) + 1) & 0x1]; +} + +/* + * Clean up this rcu_node structure's no-CBs state at the end of + * a grace period, and also return whether any no-CBs CPU associated + * with this rcu_node structure needs another grace period. + */ +static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) +{ + int c = rnp->completed; + int needmore; + + wake_up_all(&rnp->nocb_gp_wq[c & 0x1]); + rnp->n_nocb_gp_requests[c & 0x1] = 0; + needmore = rnp->n_nocb_gp_requests[(c + 1) & 0x1]; + return needmore; +} + +/* + * Set the root rcu_node structure's ->n_nocb_gp_requests field + * based on the sum of those of all rcu_node structures. This does + * double-count the root rcu_node structure's requests, but this + * is necessary to handle the possibility of a rcu_nocb_kthread() + * having awakened during the time that the rcu_node structures + * were being updated for the end of the previous grace period. */ -static int rcu_nocb_needs_gp(struct rcu_data *rdp) +static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) +{ + rnp->n_nocb_gp_requests[(rnp->completed + 1) & 0x1] += nrq; +} + +static void rcu_init_one_nocb(struct rcu_node *rnp) { - return rdp->nocb_needs_gp; + init_waitqueue_head(&rnp->nocb_gp_wq[0]); + init_waitqueue_head(&rnp->nocb_gp_wq[1]); } /* Is the specified CPU a no-CPUs CPU? */ @@ -2289,31 +2329,73 @@ static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, static void rcu_nocb_wait_gp(struct rcu_data *rdp) { unsigned long c; + bool d; unsigned long flags; - unsigned long j; + unsigned long flags1; struct rcu_node *rnp = rdp->mynode; + struct rcu_node *rnp_root = rcu_get_root(rdp->rsp); raw_spin_lock_irqsave(&rnp->lock, flags); c = rnp->completed + 2; - rdp->nocb_needs_gp = true; - raw_spin_unlock_irqrestore(&rnp->lock, flags); + + /* Count our request for a grace period. */ + rnp->n_nocb_gp_requests[c & 0x1]++; + + if (rnp->gpnum != rnp->completed) { + + /* + * This rcu_node structure believes that a grace period + * is in progress, so we are done. When this grace + * period ends, our request will be acted upon. + */ + raw_spin_unlock_irqrestore(&rnp->lock, flags); + + } else { + + /* + * Might not be a grace period, check root rcu_node + * structure to see if we must start one. + */ + if (rnp != rnp_root) + raw_spin_lock(&rnp_root->lock); /* irqs disabled. */ + if (rnp_root->gpnum != rnp_root->completed) { + raw_spin_unlock(&rnp_root->lock); /* irqs disabled. */ + } else { + + /* + * No grace period, so we need to start one. + * The good news is that we can wait for exactly + * one grace period instead of part of the current + * grace period and all of the next grace period. + * Adjust counters accordingly and start the + * needed grace period. + */ + rnp->n_nocb_gp_requests[c & 0x1]--; + c = rnp_root->completed + 1; + rnp->n_nocb_gp_requests[c & 0x1]++; + rnp_root->n_nocb_gp_requests[c & 0x1]++; + local_save_flags(flags1); + rcu_start_gp(rdp->rsp, flags1); /* Rlses ->lock. */ + } + + /* Clean up locking and irq state. */ + if (rnp != rnp_root) + raw_spin_unlock_irqrestore(&rnp->lock, flags); + else + local_irq_restore(flags); + } /* * Wait for the grace period. Do so interruptibly to avoid messing * up the load average. */ for (;;) { - j = jiffies; - schedule_timeout_interruptible(2); - raw_spin_lock_irqsave(&rnp->lock, flags); - if (ULONG_CMP_GE(rnp->completed, c)) { - rdp->nocb_needs_gp = false; - raw_spin_unlock_irqrestore(&rnp->lock, flags); + wait_event_interruptible( + rnp->nocb_gp_wq[c & 0x1], + (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c))); + if (likely(d)) break; - } - if (j == jiffies) - flush_signals(current); - raw_spin_unlock_irqrestore(&rnp->lock, flags); + flush_signals(current); } smp_mb(); /* Ensure that CB invocation happens after GP end. */ } @@ -2416,11 +2498,24 @@ static bool init_nocb_callback_list(struct rcu_data *rdp) #else /* #ifdef CONFIG_RCU_NOCB_CPU */ -static int rcu_nocb_needs_gp(struct rcu_data *rdp) +static int rcu_nocb_needs_gp(struct rcu_state *rsp) +{ + return 0; +} + +static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) { return 0; } +static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) +{ +} + +static void rcu_init_one_nocb(struct rcu_node *rnp) +{ +} + static bool is_nocb_cpu(int cpu) { return false; -- cgit v1.2.3 From a488985851cf2facd2227bd982cc2c251df56268 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 3 Dec 2012 08:16:28 -0800 Subject: rcu: Distinguish "rcuo" kthreads by RCU flavor Currently, the per-no-CBs-CPU kthreads are named "rcuo" followed by the CPU number, for example, "rcuo". This is problematic given that there are either two or three RCU flavors, each of which gets a per-CPU kthread with exactly the same name. This commit therefore introduces a one-letter abbreviation for each RCU flavor, namely 'b' for RCU-bh, 'p' for RCU-preempt, and 's' for RCU-sched. This abbreviation is used to distinguish the "rcuo" kthreads, for example, for CPU 0 we would have "rcuob/0", "rcuop/0", and "rcuos/0". Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Dietmar Eggemann --- Documentation/kernel-parameters.txt | 7 +++++-- init/Kconfig | 13 +++++++------ kernel/rcutree.c | 7 ++++--- kernel/rcutree.h | 1 + kernel/rcutree_plugin.h | 5 +++-- 5 files changed, 20 insertions(+), 13 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 4609e81dbc37..a17ba16c8fc8 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2461,9 +2461,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted. In kernels built with CONFIG_RCU_NOCB_CPU=y, set the specified list of CPUs to be no-callback CPUs. Invocation of these CPUs' RCU callbacks will - be offloaded to "rcuoN" kthreads created for - that purpose. This reduces OS jitter on the + be offloaded to "rcuox/N" kthreads created for + that purpose, where "x" is "b" for RCU-bh, "p" + for RCU-preempt, and "s" for RCU-sched, and "N" + is the CPU number. This reduces OS jitter on the offloaded CPUs, which can be useful for HPC and + real-time workloads. It can also improve energy efficiency for asymmetric multiprocessors. diff --git a/init/Kconfig b/init/Kconfig index 307499704580..717584064a7e 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -666,12 +666,13 @@ config RCU_NOCB_CPU This option offloads callback invocation from the set of CPUs specified at boot time by the rcu_nocbs parameter. - For each such CPU, a kthread ("rcuoN") will be created to - invoke callbacks, where the "N" is the CPU being offloaded. - Nothing prevents this kthread from running on the specified - CPUs, but (1) the kthreads may be preempted between each - callback, and (2) affinity or cgroups can be used to force - the kthreads to run on whatever set of CPUs is desired. + For each such CPU, a kthread ("rcuox/N") will be created to + invoke callbacks, where the "N" is the CPU being offloaded, + and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and + "s" for RCU-sched. Nothing prevents this kthread from running + on the specified CPUs, but (1) the kthreads may be preempted + between each callback, and (2) affinity or cgroups can be used + to force the kthreads to run on whatever set of CPUs is desired. Say Y here if you want to help to debug reduced OS jitter. Say N here if you are unsure. diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 433f426c848f..074cb2d974bf 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -64,7 +64,7 @@ static struct lock_class_key rcu_node_class[RCU_NUM_LVLS]; static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS]; -#define RCU_STATE_INITIALIZER(sname, cr) { \ +#define RCU_STATE_INITIALIZER(sname, sabbr, cr) { \ .level = { &sname##_state.node[0] }, \ .call = cr, \ .fqs_state = RCU_GP_IDLE, \ @@ -76,13 +76,14 @@ static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS]; .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \ .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \ .name = #sname, \ + .abbr = sabbr, \ } struct rcu_state rcu_sched_state = - RCU_STATE_INITIALIZER(rcu_sched, call_rcu_sched); + RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched); DEFINE_PER_CPU(struct rcu_data, rcu_sched_data); -struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh, call_rcu_bh); +struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh); DEFINE_PER_CPU(struct rcu_data, rcu_bh_data); static struct rcu_state *rcu_state; diff --git a/kernel/rcutree.h b/kernel/rcutree.h index e51373c0b748..b6c2335efbdf 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -443,6 +443,7 @@ struct rcu_state { unsigned long gp_max; /* Maximum GP duration in */ /* jiffies. */ char *name; /* Name of structure. */ + char abbr; /* Abbreviated name. */ struct list_head flavors; /* List of RCU flavors. */ }; diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index e32236e83dda..c0164441ab92 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -111,7 +111,7 @@ static void __init rcu_bootup_announce_oddness(void) #ifdef CONFIG_TREE_PREEMPT_RCU struct rcu_state rcu_preempt_state = - RCU_STATE_INITIALIZER(rcu_preempt, call_rcu); + RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); static struct rcu_state *rcu_state = &rcu_preempt_state; @@ -2517,7 +2517,8 @@ static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) return; for_each_cpu(cpu, rcu_nocb_mask) { rdp = per_cpu_ptr(rsp->rda, cpu); - t = kthread_run(rcu_nocb_kthread, rdp, "rcuo%d", cpu); + t = kthread_run(rcu_nocb_kthread, rdp, + "rcuo%c/%d", rsp->abbr, cpu); BUG_ON(IS_ERR(t)); ACCESS_ONCE(rdp->nocb_kthread) = t; } -- cgit v1.2.3 From b11cc5760a9c48c870ad286e8a6d8fdb998fa58d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 17 Dec 2012 14:21:14 -0800 Subject: rcu: Accelerate RCU callbacks at grace-period end Now that callback acceleration is idempotent, it is safe to accelerate callbacks during grace-period cleanup on any CPUs that the kthread happens to be running on. This commit therefore propagates the completion of the grace period to the per-CPU data structures, and also adds an rcu_advance_cbs() just before the cpu_needs_another_gp() check in order to reduce false-positive grace periods. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 074cb2d974bf..2015bce749f9 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1396,6 +1396,9 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) rcu_for_each_node_breadth_first(rsp, rnp) { raw_spin_lock_irq(&rnp->lock); rnp->completed = rsp->gpnum; + rdp = this_cpu_ptr(rsp->rda); + if (rnp == rdp->mynode) + __rcu_process_gp_end(rsp, rnp, rdp); nocb += rcu_nocb_gp_cleanup(rsp, rnp); raw_spin_unlock_irq(&rnp->lock); cond_resched(); @@ -1408,6 +1411,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) trace_rcu_grace_period(rsp->name, rsp->completed, "end"); rsp->fqs_state = RCU_GP_IDLE; rdp = this_cpu_ptr(rsp->rda); + rcu_advance_cbs(rsp, rnp, rdp); /* Reduce false positives below. */ if (cpu_needs_another_gp(rsp, rdp)) rsp->gp_flags = 1; raw_spin_unlock_irq(&rnp->lock); @@ -1497,6 +1501,15 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) struct rcu_data *rdp = this_cpu_ptr(rsp->rda); struct rcu_node *rnp = rcu_get_root(rsp); + /* + * If there is no grace period in progress right now, any + * callbacks we have up to this point will be satisfied by the + * next grace period. Also, advancing the callbacks reduces the + * probability of false positives from cpu_needs_another_gp() + * resulting in pointless grace periods. So, advance callbacks! + */ + rcu_advance_cbs(rsp, rnp, rdp); + if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) { /* @@ -1509,14 +1522,6 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) return; } - /* - * Because there is no grace period in progress right now, - * any callbacks we have up to this point will be satisfied - * by the next grace period. So this is a good place to - * assign a grace period number to recently posted callbacks. - */ - rcu_accelerate_cbs(rsp, rnp, rdp); - rsp->gp_flags = RCU_GP_FLAG_INIT; raw_spin_unlock(&rnp->lock); /* Interrupts remain disabled. */ -- cgit v1.2.3 From c0f4dfd4f90f1667d234d21f15153ea09a2eaa66 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 28 Dec 2012 11:30:36 -0800 Subject: rcu: Make RCU_FAST_NO_HZ take advantage of numbered callbacks Because RCU callbacks are now associated with the number of the grace period that they must wait for, CPUs can now take advance callbacks corresponding to grace periods that ended while a given CPU was in dyntick-idle mode. This eliminates the need to try forcing the RCU state machine while entering idle, thus reducing the CPU intensiveness of RCU_FAST_NO_HZ, which should increase its energy efficiency. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- Documentation/kernel-parameters.txt | 28 ++- include/linux/rcupdate.h | 1 + init/Kconfig | 17 +- kernel/rcutree.c | 28 +-- kernel/rcutree.h | 12 +- kernel/rcutree_plugin.h | 374 ++++++++++-------------------------- kernel/rcutree_trace.c | 2 - 7 files changed, 149 insertions(+), 313 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index a17ba16c8fc8..22303b2e74bc 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2490,6 +2490,17 @@ bytes respectively. Such letter suffixes can also be entirely omitted. leaf rcu_node structure. Useful for very large systems. + rcutree.jiffies_till_first_fqs= [KNL,BOOT] + Set delay from grace-period initialization to + first attempt to force quiescent states. + Units are jiffies, minimum value is zero, + and maximum value is HZ. + + rcutree.jiffies_till_next_fqs= [KNL,BOOT] + Set delay between subsequent attempts to force + quiescent states. Units are jiffies, minimum + value is one, and maximum value is HZ. + rcutree.qhimark= [KNL,BOOT] Set threshold of queued RCU callbacks over which batch limiting is disabled. @@ -2504,16 +2515,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted. rcutree.rcu_cpu_stall_timeout= [KNL,BOOT] Set timeout for RCU CPU stall warning messages. - rcutree.jiffies_till_first_fqs= [KNL,BOOT] - Set delay from grace-period initialization to - first attempt to force quiescent states. - Units are jiffies, minimum value is zero, - and maximum value is HZ. + rcutree.rcu_idle_gp_delay= [KNL,BOOT] + Set wakeup interval for idle CPUs that have + RCU callbacks (RCU_FAST_NO_HZ=y). - rcutree.jiffies_till_next_fqs= [KNL,BOOT] - Set delay between subsequent attempts to force - quiescent states. Units are jiffies, minimum - value is one, and maximum value is HZ. + rcutree.rcu_idle_lazy_gp_delay= [KNL,BOOT] + Set wakeup interval for idle CPUs that have + only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). + Lazy RCU callbacks are those which RCU can + prove do nothing more than free memory. rcutorture.fqs_duration= [KNL,BOOT] Set duration of force_quiescent_state bursts. diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index b758ce17b309..9ed2c9a4de45 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -80,6 +80,7 @@ extern void do_trace_rcu_torture_read(char *rcutorturename, #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) +#define ulong2long(a) (*(long *)(&(a))) /* Exported common interfaces */ diff --git a/init/Kconfig b/init/Kconfig index 717584064a7e..a3a2304fa6d2 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -582,13 +582,16 @@ config RCU_FAST_NO_HZ depends on NO_HZ && SMP default n help - This option causes RCU to attempt to accelerate grace periods in - order to allow CPUs to enter dynticks-idle state more quickly. - On the other hand, this option increases the overhead of the - dynticks-idle checking, thus degrading scheduling latency. - - Say Y if energy efficiency is critically important, and you don't - care about real-time response. + This option permits CPUs to enter dynticks-idle state even if + they have RCU callbacks queued, and prevents RCU from waking + these CPUs up more than roughly once every four jiffies (by + default, you can adjust this using the rcutree.rcu_idle_gp_delay + parameter), thus improving energy efficiency. On the other + hand, this option increases the duration of RCU grace periods, + for example, slowing down synchronize_rcu(). + + Say Y if energy efficiency is critically important, and you + don't care about increased grace-period durations. Say N if you are unsure. diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 2015bce749f9..7b1d7769872a 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2640,19 +2640,27 @@ static int rcu_pending(int cpu) } /* - * Check to see if any future RCU-related work will need to be done - * by the current CPU, even if none need be done immediately, returning - * 1 if so. + * Return true if the specified CPU has any callback. If all_lazy is + * non-NULL, store an indication of whether all callbacks are lazy. + * (If there are no callbacks, all of them are deemed to be lazy.) */ -static int rcu_cpu_has_callbacks(int cpu) +static int rcu_cpu_has_callbacks(int cpu, bool *all_lazy) { + bool al = true; + bool hc = false; + struct rcu_data *rdp; struct rcu_state *rsp; - /* RCU callbacks either ready or pending? */ - for_each_rcu_flavor(rsp) - if (per_cpu_ptr(rsp->rda, cpu)->nxtlist) - return 1; - return 0; + for_each_rcu_flavor(rsp) { + rdp = per_cpu_ptr(rsp->rda, cpu); + if (rdp->qlen != rdp->qlen_lazy) + al = false; + if (rdp->nxtlist) + hc = true; + } + if (all_lazy) + *all_lazy = al; + return hc; } /* @@ -2871,7 +2879,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; atomic_set(&rdp->dynticks->dynticks, (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1); - rcu_prepare_for_idle_init(cpu); raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ /* Add CPU to rcu_node bitmasks. */ @@ -2945,7 +2952,6 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, */ for_each_rcu_flavor(rsp) rcu_cleanup_dying_cpu(rsp); - rcu_cleanup_after_idle(cpu); break; case CPU_DEAD: case CPU_DEAD_FROZEN: diff --git a/kernel/rcutree.h b/kernel/rcutree.h index b6c2335efbdf..96a27f922e92 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -88,18 +88,13 @@ struct rcu_dynticks { int dynticks_nmi_nesting; /* Track NMI nesting level. */ atomic_t dynticks; /* Even value for idle, else odd. */ #ifdef CONFIG_RCU_FAST_NO_HZ - int dyntick_drain; /* Prepare-for-idle state variable. */ - unsigned long dyntick_holdoff; - /* No retries for the jiffy of failure. */ - struct timer_list idle_gp_timer; - /* Wake up CPU sleeping with callbacks. */ - unsigned long idle_gp_timer_expires; - /* When to wake up CPU (for repost). */ - bool idle_first_pass; /* First pass of attempt to go idle? */ + bool all_lazy; /* Are all CPU's CBs lazy? */ unsigned long nonlazy_posted; /* # times non-lazy CBs posted to CPU. */ unsigned long nonlazy_posted_snap; /* idle-period nonlazy_posted snapshot. */ + unsigned long last_accelerate; + /* Last jiffy CBs were accelerated. */ int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */ #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */ }; @@ -521,7 +516,6 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, struct rcu_node *rnp); #endif /* #ifdef CONFIG_RCU_BOOST */ static void __cpuinit rcu_prepare_kthreads(int cpu); -static void rcu_prepare_for_idle_init(int cpu); static void rcu_cleanup_after_idle(int cpu); static void rcu_prepare_for_idle(int cpu); static void rcu_idle_count_callbacks_posted(void); diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 28185ad18df3..d318f9f18be5 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -1543,14 +1543,7 @@ static void __cpuinit rcu_prepare_kthreads(int cpu) int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) { *delta_jiffies = ULONG_MAX; - return rcu_cpu_has_callbacks(cpu); -} - -/* - * Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it. - */ -static void rcu_prepare_for_idle_init(int cpu) -{ + return rcu_cpu_has_callbacks(cpu, NULL); } /* @@ -1587,16 +1580,6 @@ static void rcu_idle_count_callbacks_posted(void) * * The following three proprocessor symbols control this state machine: * - * RCU_IDLE_FLUSHES gives the maximum number of times that we will attempt - * to satisfy RCU. Beyond this point, it is better to incur a periodic - * scheduling-clock interrupt than to loop through the state machine - * at full power. - * RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are - * optional if RCU does not need anything immediately from this - * CPU, even if this CPU still has RCU callbacks queued. The first - * times through the state machine are mandatory: we need to give - * the state machine a chance to communicate a quiescent state - * to the RCU core. * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted * to sleep in dyntick-idle mode with RCU callbacks pending. This * is sized to be roughly one RCU grace period. Those energy-efficiency @@ -1612,15 +1595,9 @@ static void rcu_idle_count_callbacks_posted(void) * adjustment, they can be converted into kernel config parameters, though * making the state machine smarter might be a better option. */ -#define RCU_IDLE_FLUSHES 5 /* Number of dyntick-idle tries. */ -#define RCU_IDLE_OPT_FLUSHES 3 /* Optional dyntick-idle tries. */ #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ -static int rcu_idle_flushes = RCU_IDLE_FLUSHES; -module_param(rcu_idle_flushes, int, 0644); -static int rcu_idle_opt_flushes = RCU_IDLE_OPT_FLUSHES; -module_param(rcu_idle_opt_flushes, int, 0644); static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; module_param(rcu_idle_gp_delay, int, 0644); static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; @@ -1629,178 +1606,97 @@ module_param(rcu_idle_lazy_gp_delay, int, 0644); extern int tick_nohz_enabled; /* - * Does the specified flavor of RCU have non-lazy callbacks pending on - * the specified CPU? Both RCU flavor and CPU are specified by the - * rcu_data structure. - */ -static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp) -{ - return rdp->qlen != rdp->qlen_lazy; -} - -#ifdef CONFIG_TREE_PREEMPT_RCU - -/* - * Are there non-lazy RCU-preempt callbacks? (There cannot be if there - * is no RCU-preempt in the kernel.) + * Try to advance callbacks for all flavors of RCU on the current CPU. + * Afterwards, if there are any callbacks ready for immediate invocation, + * return true. */ -static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu) +static bool rcu_try_advance_all_cbs(void) { - struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); - - return __rcu_cpu_has_nonlazy_callbacks(rdp); -} - -#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ + bool cbs_ready = false; + struct rcu_data *rdp; + struct rcu_node *rnp; + struct rcu_state *rsp; -static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu) -{ - return 0; -} + for_each_rcu_flavor(rsp) { + rdp = this_cpu_ptr(rsp->rda); + rnp = rdp->mynode; -#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */ + /* + * Don't bother checking unless a grace period has + * completed since we last checked and there are + * callbacks not yet ready to invoke. + */ + if (rdp->completed != rnp->completed && + rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]) + rcu_process_gp_end(rsp, rdp); -/* - * Does any flavor of RCU have non-lazy callbacks on the specified CPU? - */ -static bool rcu_cpu_has_nonlazy_callbacks(int cpu) -{ - return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) || - __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) || - rcu_preempt_cpu_has_nonlazy_callbacks(cpu); + if (cpu_has_callbacks_ready_to_invoke(rdp)) + cbs_ready = true; + } + return cbs_ready; } /* - * Allow the CPU to enter dyntick-idle mode if either: (1) There are no - * callbacks on this CPU, (2) this CPU has not yet attempted to enter - * dyntick-idle mode, or (3) this CPU is in the process of attempting to - * enter dyntick-idle mode. Otherwise, if we have recently tried and failed - * to enter dyntick-idle mode, we refuse to try to enter it. After all, - * it is better to incur scheduling-clock interrupts than to spin - * continuously for the same time duration! + * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready + * to invoke. If the CPU has callbacks, try to advance them. Tell the + * caller to set the timeout based on whether or not there are non-lazy + * callbacks. * - * The delta_jiffies argument is used to store the time when RCU is - * going to need the CPU again if it still has callbacks. The reason - * for this is that rcu_prepare_for_idle() might need to post a timer, - * but if so, it will do so after tick_nohz_stop_sched_tick() has set - * the wakeup time for this CPU. This means that RCU's timer can be - * delayed until the wakeup time, which defeats the purpose of posting - * a timer. + * The caller must have disabled interrupts. */ -int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) +int rcu_needs_cpu(int cpu, unsigned long *dj) { struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); - /* Flag a new idle sojourn to the idle-entry state machine. */ - rdtp->idle_first_pass = 1; + /* Snapshot to detect later posting of non-lazy callback. */ + rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; + /* If no callbacks, RCU doesn't need the CPU. */ - if (!rcu_cpu_has_callbacks(cpu)) { - *delta_jiffies = ULONG_MAX; + if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) { + *dj = ULONG_MAX; return 0; } - if (rdtp->dyntick_holdoff == jiffies) { - /* RCU recently tried and failed, so don't try again. */ - *delta_jiffies = 1; + + /* Attempt to advance callbacks. */ + if (rcu_try_advance_all_cbs()) { + /* Some ready to invoke, so initiate later invocation. */ + invoke_rcu_core(); return 1; } - /* Set up for the possibility that RCU will post a timer. */ - if (rcu_cpu_has_nonlazy_callbacks(cpu)) { - *delta_jiffies = round_up(rcu_idle_gp_delay + jiffies, - rcu_idle_gp_delay) - jiffies; + rdtp->last_accelerate = jiffies; + + /* Request timer delay depending on laziness, and round. */ + if (rdtp->all_lazy) { + *dj = round_up(rcu_idle_gp_delay + jiffies, + rcu_idle_gp_delay) - jiffies; } else { - *delta_jiffies = jiffies + rcu_idle_lazy_gp_delay; - *delta_jiffies = round_jiffies(*delta_jiffies) - jiffies; + *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; } return 0; } /* - * Handler for smp_call_function_single(). The only point of this - * handler is to wake the CPU up, so the handler does only tracing. - */ -void rcu_idle_demigrate(void *unused) -{ - trace_rcu_prep_idle("Demigrate"); -} - -/* - * Timer handler used to force CPU to start pushing its remaining RCU - * callbacks in the case where it entered dyntick-idle mode with callbacks - * pending. The hander doesn't really need to do anything because the - * real work is done upon re-entry to idle, or by the next scheduling-clock - * interrupt should idle not be re-entered. - * - * One special case: the timer gets migrated without awakening the CPU - * on which the timer was scheduled on. In this case, we must wake up - * that CPU. We do so with smp_call_function_single(). - */ -static void rcu_idle_gp_timer_func(unsigned long cpu_in) -{ - int cpu = (int)cpu_in; - - trace_rcu_prep_idle("Timer"); - if (cpu != smp_processor_id()) - smp_call_function_single(cpu, rcu_idle_demigrate, NULL, 0); - else - WARN_ON_ONCE(1); /* Getting here can hang the system... */ -} - -/* - * Initialize the timer used to pull CPUs out of dyntick-idle mode. - */ -static void rcu_prepare_for_idle_init(int cpu) -{ - struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); - - rdtp->dyntick_holdoff = jiffies - 1; - setup_timer(&rdtp->idle_gp_timer, rcu_idle_gp_timer_func, cpu); - rdtp->idle_gp_timer_expires = jiffies - 1; - rdtp->idle_first_pass = 1; -} - -/* - * Clean up for exit from idle. Because we are exiting from idle, there - * is no longer any point to ->idle_gp_timer, so cancel it. This will - * do nothing if this timer is not active, so just cancel it unconditionally. - */ -static void rcu_cleanup_after_idle(int cpu) -{ - struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); - - del_timer(&rdtp->idle_gp_timer); - trace_rcu_prep_idle("Cleanup after idle"); - rdtp->tick_nohz_enabled_snap = ACCESS_ONCE(tick_nohz_enabled); -} - -/* - * Check to see if any RCU-related work can be done by the current CPU, - * and if so, schedule a softirq to get it done. This function is part - * of the RCU implementation; it is -not- an exported member of the RCU API. - * - * The idea is for the current CPU to clear out all work required by the - * RCU core for the current grace period, so that this CPU can be permitted - * to enter dyntick-idle mode. In some cases, it will need to be awakened - * at the end of the grace period by whatever CPU ends the grace period. - * This allows CPUs to go dyntick-idle more quickly, and to reduce the - * number of wakeups by a modest integer factor. - * - * Because it is not legal to invoke rcu_process_callbacks() with irqs - * disabled, we do one pass of force_quiescent_state(), then do a - * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked - * later. The ->dyntick_drain field controls the sequencing. + * Prepare a CPU for idle from an RCU perspective. The first major task + * is to sense whether nohz mode has been enabled or disabled via sysfs. + * The second major task is to check to see if a non-lazy callback has + * arrived at a CPU that previously had only lazy callbacks. The third + * major task is to accelerate (that is, assign grace-period numbers to) + * any recently arrived callbacks. * * The caller must have disabled interrupts. */ static void rcu_prepare_for_idle(int cpu) { - struct timer_list *tp; + struct rcu_data *rdp; struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); + struct rcu_node *rnp; + struct rcu_state *rsp; int tne; /* Handle nohz enablement switches conservatively. */ tne = ACCESS_ONCE(tick_nohz_enabled); if (tne != rdtp->tick_nohz_enabled_snap) { - if (rcu_cpu_has_callbacks(cpu)) + if (rcu_cpu_has_callbacks(cpu, NULL)) invoke_rcu_core(); /* force nohz to see update. */ rdtp->tick_nohz_enabled_snap = tne; return; @@ -1808,125 +1704,56 @@ static void rcu_prepare_for_idle(int cpu) if (!tne) return; - /* Adaptive-tick mode, where usermode execution is idle to RCU. */ - if (!is_idle_task(current)) { - rdtp->dyntick_holdoff = jiffies - 1; - if (rcu_cpu_has_nonlazy_callbacks(cpu)) { - trace_rcu_prep_idle("User dyntick with callbacks"); - rdtp->idle_gp_timer_expires = - round_up(jiffies + rcu_idle_gp_delay, - rcu_idle_gp_delay); - } else if (rcu_cpu_has_callbacks(cpu)) { - rdtp->idle_gp_timer_expires = - round_jiffies(jiffies + rcu_idle_lazy_gp_delay); - trace_rcu_prep_idle("User dyntick with lazy callbacks"); - } else { - return; - } - tp = &rdtp->idle_gp_timer; - mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); + /* If this is a no-CBs CPU, no callbacks, just return. */ + if (is_nocb_cpu(cpu)) return; - } /* - * If this is an idle re-entry, for example, due to use of - * RCU_NONIDLE() or the new idle-loop tracing API within the idle - * loop, then don't take any state-machine actions, unless the - * momentary exit from idle queued additional non-lazy callbacks. - * Instead, repost the ->idle_gp_timer if this CPU has callbacks - * pending. + * If a non-lazy callback arrived at a CPU having only lazy + * callbacks, invoke RCU core for the side-effect of recalculating + * idle duration on re-entry to idle. */ - if (!rdtp->idle_first_pass && - (rdtp->nonlazy_posted == rdtp->nonlazy_posted_snap)) { - if (rcu_cpu_has_callbacks(cpu)) { - tp = &rdtp->idle_gp_timer; - mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); - } + if (rdtp->all_lazy && + rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) { + invoke_rcu_core(); return; } - rdtp->idle_first_pass = 0; - rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted - 1; /* - * If there are no callbacks on this CPU, enter dyntick-idle mode. - * Also reset state to avoid prejudicing later attempts. + * If we have not yet accelerated this jiffy, accelerate all + * callbacks on this CPU. */ - if (!rcu_cpu_has_callbacks(cpu)) { - rdtp->dyntick_holdoff = jiffies - 1; - rdtp->dyntick_drain = 0; - trace_rcu_prep_idle("No callbacks"); + if (rdtp->last_accelerate == jiffies) return; + rdtp->last_accelerate = jiffies; + for_each_rcu_flavor(rsp) { + rdp = per_cpu_ptr(rsp->rda, cpu); + if (!*rdp->nxttail[RCU_DONE_TAIL]) + continue; + rnp = rdp->mynode; + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + rcu_accelerate_cbs(rsp, rnp, rdp); + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ } +} - /* - * If in holdoff mode, just return. We will presumably have - * refrained from disabling the scheduling-clock tick. - */ - if (rdtp->dyntick_holdoff == jiffies) { - trace_rcu_prep_idle("In holdoff"); - return; - } +/* + * Clean up for exit from idle. Attempt to advance callbacks based on + * any grace periods that elapsed while the CPU was idle, and if any + * callbacks are now ready to invoke, initiate invocation. + */ +static void rcu_cleanup_after_idle(int cpu) +{ + struct rcu_data *rdp; + struct rcu_state *rsp; - /* Check and update the ->dyntick_drain sequencing. */ - if (rdtp->dyntick_drain <= 0) { - /* First time through, initialize the counter. */ - rdtp->dyntick_drain = rcu_idle_flushes; - } else if (rdtp->dyntick_drain <= rcu_idle_opt_flushes && - !rcu_pending(cpu) && - !local_softirq_pending()) { - /* Can we go dyntick-idle despite still having callbacks? */ - rdtp->dyntick_drain = 0; - rdtp->dyntick_holdoff = jiffies; - if (rcu_cpu_has_nonlazy_callbacks(cpu)) { - trace_rcu_prep_idle("Dyntick with callbacks"); - rdtp->idle_gp_timer_expires = - round_up(jiffies + rcu_idle_gp_delay, - rcu_idle_gp_delay); - } else { - rdtp->idle_gp_timer_expires = - round_jiffies(jiffies + rcu_idle_lazy_gp_delay); - trace_rcu_prep_idle("Dyntick with lazy callbacks"); - } - tp = &rdtp->idle_gp_timer; - mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); - rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; - return; /* Nothing more to do immediately. */ - } else if (--(rdtp->dyntick_drain) <= 0) { - /* We have hit the limit, so time to give up. */ - rdtp->dyntick_holdoff = jiffies; - trace_rcu_prep_idle("Begin holdoff"); - invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */ + if (is_nocb_cpu(cpu)) return; - } - - /* - * Do one step of pushing the remaining RCU callbacks through - * the RCU core state machine. - */ -#ifdef CONFIG_TREE_PREEMPT_RCU - if (per_cpu(rcu_preempt_data, cpu).nxtlist) { - rcu_preempt_qs(cpu); - force_quiescent_state(&rcu_preempt_state); - } -#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ - if (per_cpu(rcu_sched_data, cpu).nxtlist) { - rcu_sched_qs(cpu); - force_quiescent_state(&rcu_sched_state); - } - if (per_cpu(rcu_bh_data, cpu).nxtlist) { - rcu_bh_qs(cpu); - force_quiescent_state(&rcu_bh_state); - } - - /* - * If RCU callbacks are still pending, RCU still needs this CPU. - * So try forcing the callbacks through the grace period. - */ - if (rcu_cpu_has_callbacks(cpu)) { - trace_rcu_prep_idle("More callbacks"); - invoke_rcu_core(); - } else { - trace_rcu_prep_idle("Callbacks drained"); + rcu_try_advance_all_cbs(); + for_each_rcu_flavor(rsp) { + rdp = per_cpu_ptr(rsp->rda, cpu); + if (cpu_has_callbacks_ready_to_invoke(rdp)) + invoke_rcu_core(); } } @@ -2034,16 +1861,13 @@ early_initcall(rcu_register_oom_notifier); static void print_cpu_stall_fast_no_hz(char *cp, int cpu) { struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); - struct timer_list *tltp = &rdtp->idle_gp_timer; - char c; + unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap; - c = rdtp->dyntick_holdoff == jiffies ? 'H' : '.'; - if (timer_pending(tltp)) - sprintf(cp, "drain=%d %c timer=%lu", - rdtp->dyntick_drain, c, tltp->expires - jiffies); - else - sprintf(cp, "drain=%d %c timer not pending", - rdtp->dyntick_drain, c); + sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", + rdtp->last_accelerate & 0xffff, jiffies & 0xffff, + ulong2long(nlpd), + rdtp->all_lazy ? 'L' : '.', + rdtp->tick_nohz_enabled_snap ? '.' : 'D'); } #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c index 0d095dcaa670..49099e81c87b 100644 --- a/kernel/rcutree_trace.c +++ b/kernel/rcutree_trace.c @@ -46,8 +46,6 @@ #define RCU_TREE_NONCORE #include "rcutree.h" -#define ulong2long(a) (*(long *)(&(a))) - static int r_open(struct inode *inode, struct file *file, const struct seq_operations *op) { -- cgit v1.2.3 From b92db6cb7efcbd41e469e1d757c47da4865f7622 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 29 Dec 2012 14:52:41 -0800 Subject: rcu: Rearrange locking in rcu_start_gp() If CPUs are to give prior notice of needed grace periods, it will be necessary to invoke rcu_start_gp() without dropping the root rcu_node structure's ->lock. This commit takes a first step in this direction by moving the release of this lock to the end of rcu_start_gp(). Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 7b1d7769872a..2c6a9314c7f7 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1521,16 +1521,14 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } - rsp->gp_flags = RCU_GP_FLAG_INIT; - raw_spin_unlock(&rnp->lock); /* Interrupts remain disabled. */ /* Ensure that CPU is aware of completion of last grace period. */ - rcu_process_gp_end(rsp, rdp); - local_irq_restore(flags); + __rcu_process_gp_end(rsp, rdp->mynode, rdp); /* Wake up rcu_gp_kthread() to start the grace period. */ wake_up(&rsp->gp_wq); + raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* -- cgit v1.2.3 From b8462084a2a88a6a0489f9bb7d8b1bb95bc455ab Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 29 Dec 2012 22:04:18 -0800 Subject: rcu: Push lock release to rcu_start_gp()'s callers If CPUs are to give prior notice of needed grace periods, it will be necessary to invoke rcu_start_gp() without dropping the root rcu_node structure's ->lock. This commit takes a second step in this direction by moving the release of this lock to rcu_start_gp()'s callers. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 24 ++++++++++-------------- kernel/rcutree_plugin.h | 5 ++--- 2 files changed, 12 insertions(+), 17 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 2c6a9314c7f7..0d532950baa3 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1487,16 +1487,14 @@ static int __noreturn rcu_gp_kthread(void *arg) /* * Start a new RCU grace period if warranted, re-initializing the hierarchy * in preparation for detecting the next grace period. The caller must hold - * the root node's ->lock, which is released before return. Hard irqs must - * be disabled. + * the root node's ->lock and hard irqs must be disabled. * * Note that it is legal for a dying CPU (which is marked as offline) to * invoke this function. This can happen when the dying CPU reports its * quiescent state. */ static void -rcu_start_gp(struct rcu_state *rsp, unsigned long flags) - __releases(rcu_get_root(rsp)->lock) +rcu_start_gp(struct rcu_state *rsp) { struct rcu_data *rdp = this_cpu_ptr(rsp->rda); struct rcu_node *rnp = rcu_get_root(rsp); @@ -1510,15 +1508,13 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) */ rcu_advance_cbs(rsp, rnp, rdp); - if (!rsp->gp_kthread || - !cpu_needs_another_gp(rsp, rdp)) { + if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) { /* * Either we have not yet spawned the grace-period * task, this CPU does not need another grace period, * or a grace period is already in progress. * Either way, don't start a new grace period. */ - raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } rsp->gp_flags = RCU_GP_FLAG_INIT; @@ -1528,15 +1524,14 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) /* Wake up rcu_gp_kthread() to start the grace period. */ wake_up(&rsp->gp_wq); - raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* * Report a full set of quiescent states to the specified rcu_state * data structure. This involves cleaning up after the prior grace * period and letting rcu_start_gp() start up the next grace period - * if one is needed. Note that the caller must hold rnp->lock, as - * required by rcu_start_gp(), which will release it. + * if one is needed. Note that the caller must hold rnp->lock, which + * is released before return. */ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) @@ -2134,7 +2129,8 @@ __rcu_process_callbacks(struct rcu_state *rsp) local_irq_save(flags); if (cpu_needs_another_gp(rsp, rdp)) { raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */ - rcu_start_gp(rsp, flags); /* releases above lock */ + rcu_start_gp(rsp); + raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags); } else { local_irq_restore(flags); } @@ -2214,11 +2210,11 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp, /* Start a new grace period if one not already started. */ if (!rcu_gp_in_progress(rsp)) { - unsigned long nestflag; struct rcu_node *rnp_root = rcu_get_root(rsp); - raw_spin_lock_irqsave(&rnp_root->lock, nestflag); - rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */ + raw_spin_lock(&rnp_root->lock); + rcu_start_gp(rsp); + raw_spin_unlock(&rnp_root->lock); } else { /* Give the grace period a kick. */ rdp->blimit = LONG_MAX; diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index df50502eca2c..073ded26e259 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2174,7 +2174,6 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp) unsigned long c; bool d; unsigned long flags; - unsigned long flags1; struct rcu_node *rnp = rdp->mynode; struct rcu_node *rnp_root = rcu_get_root(rdp->rsp); @@ -2236,8 +2235,8 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp) c, rnp->level, rnp->grplo, rnp->grphi, "Startedroot"); - local_save_flags(flags1); - rcu_start_gp(rdp->rsp, flags1); /* Rlses ->lock. */ + rcu_start_gp(rdp->rsp); + raw_spin_unlock(&rnp->lock); } /* Clean up locking and irq state. */ -- cgit v1.2.3 From 0446be489795d8bb994125a916ef03211f539e54 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 30 Dec 2012 15:21:01 -0800 Subject: rcu: Abstract rcu_start_future_gp() from rcu_nocb_wait_gp() CPUs going idle will need to record the need for a future grace period, but won't actually need to block waiting on it. This commit therefore splits rcu_start_future_gp(), which does the recording, from rcu_nocb_wait_gp(), which now invokes rcu_start_future_gp() to do the recording, after which rcu_nocb_wait_gp() does the waiting. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 123 ++++++++++++++++++++++++++++++++++++++++++++++-- kernel/rcutree.h | 2 +- kernel/rcutree_plugin.h | 104 ++++------------------------------------ 3 files changed, 130 insertions(+), 99 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 0d532950baa3..f4b23f16677a 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -224,6 +224,7 @@ static ulong jiffies_till_next_fqs = RCU_JIFFIES_TILL_FORCE_QS; module_param(jiffies_till_first_fqs, ulong, 0644); module_param(jiffies_till_next_fqs, ulong, 0644); +static void rcu_start_gp(struct rcu_state *rsp); static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)); static void force_quiescent_state(struct rcu_state *rsp); static int rcu_pending(int cpu); @@ -1074,6 +1075,120 @@ static unsigned long rcu_cbs_completed(struct rcu_state *rsp, return rnp->completed + 2; } +/* + * Trace-event helper function for rcu_start_future_gp() and + * rcu_nocb_wait_gp(). + */ +static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp, + unsigned long c, char *s) +{ + trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum, + rnp->completed, c, rnp->level, + rnp->grplo, rnp->grphi, s); +} + +/* + * Start some future grace period, as needed to handle newly arrived + * callbacks. The required future grace periods are recorded in each + * rcu_node structure's ->need_future_gp field. + * + * The caller must hold the specified rcu_node structure's ->lock. + */ +static unsigned long __maybe_unused +rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp) +{ + unsigned long c; + int i; + struct rcu_node *rnp_root = rcu_get_root(rdp->rsp); + + /* + * Pick up grace-period number for new callbacks. If this + * grace period is already marked as needed, return to the caller. + */ + c = rcu_cbs_completed(rdp->rsp, rnp); + trace_rcu_future_gp(rnp, rdp, c, "Startleaf"); + if (rnp->need_future_gp[c & 0x1]) { + trace_rcu_future_gp(rnp, rdp, c, "Prestartleaf"); + return c; + } + + /* + * If either this rcu_node structure or the root rcu_node structure + * believe that a grace period is in progress, then we must wait + * for the one following, which is in "c". Because our request + * will be noticed at the end of the current grace period, we don't + * need to explicitly start one. + */ + if (rnp->gpnum != rnp->completed || + ACCESS_ONCE(rnp->gpnum) != ACCESS_ONCE(rnp->completed)) { + rnp->need_future_gp[c & 0x1]++; + trace_rcu_future_gp(rnp, rdp, c, "Startedleaf"); + return c; + } + + /* + * There might be no grace period in progress. If we don't already + * hold it, acquire the root rcu_node structure's lock in order to + * start one (if needed). + */ + if (rnp != rnp_root) + raw_spin_lock(&rnp_root->lock); + + /* + * Get a new grace-period number. If there really is no grace + * period in progress, it will be smaller than the one we obtained + * earlier. Adjust callbacks as needed. Note that even no-CBs + * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed. + */ + c = rcu_cbs_completed(rdp->rsp, rnp_root); + for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++) + if (ULONG_CMP_LT(c, rdp->nxtcompleted[i])) + rdp->nxtcompleted[i] = c; + + /* + * If the needed for the required grace period is already + * recorded, trace and leave. + */ + if (rnp_root->need_future_gp[c & 0x1]) { + trace_rcu_future_gp(rnp, rdp, c, "Prestartedroot"); + goto unlock_out; + } + + /* Record the need for the future grace period. */ + rnp_root->need_future_gp[c & 0x1]++; + + /* If a grace period is not already in progress, start one. */ + if (rnp_root->gpnum != rnp_root->completed) { + trace_rcu_future_gp(rnp, rdp, c, "Startedleafroot"); + } else { + trace_rcu_future_gp(rnp, rdp, c, "Startedroot"); + rcu_start_gp(rdp->rsp); + } +unlock_out: + if (rnp != rnp_root) + raw_spin_unlock(&rnp_root->lock); + return c; +} + +/* + * Clean up any old requests for the just-ended grace period. Also return + * whether any additional grace periods have been requested. Also invoke + * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads + * waiting for this grace period to complete. + */ +static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) +{ + int c = rnp->completed; + int needmore; + struct rcu_data *rdp = this_cpu_ptr(rsp->rda); + + rcu_nocb_gp_cleanup(rsp, rnp); + rnp->need_future_gp[c & 0x1] = 0; + needmore = rnp->need_future_gp[(c + 1) & 0x1]; + trace_rcu_future_gp(rnp, rdp, c, needmore ? "CleanupMore" : "Cleanup"); + return needmore; +} + /* * If there is room, assign a ->completed number to any callbacks on * this CPU that have not already been assigned. Also accelerate any @@ -1312,9 +1427,9 @@ static int rcu_gp_init(struct rcu_state *rsp) rdp = this_cpu_ptr(rsp->rda); rcu_preempt_check_blocked_tasks(rnp); rnp->qsmask = rnp->qsmaskinit; - rnp->gpnum = rsp->gpnum; + ACCESS_ONCE(rnp->gpnum) = rsp->gpnum; WARN_ON_ONCE(rnp->completed != rsp->completed); - rnp->completed = rsp->completed; + ACCESS_ONCE(rnp->completed) = rsp->completed; if (rnp == rdp->mynode) rcu_start_gp_per_cpu(rsp, rnp, rdp); rcu_preempt_boost_start_gp(rnp); @@ -1395,11 +1510,11 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) */ rcu_for_each_node_breadth_first(rsp, rnp) { raw_spin_lock_irq(&rnp->lock); - rnp->completed = rsp->gpnum; + ACCESS_ONCE(rnp->completed) = rsp->gpnum; rdp = this_cpu_ptr(rsp->rda); if (rnp == rdp->mynode) __rcu_process_gp_end(rsp, rnp, rdp); - nocb += rcu_nocb_gp_cleanup(rsp, rnp); + nocb += rcu_future_gp_cleanup(rsp, rnp); raw_spin_unlock_irq(&rnp->lock); cond_resched(); } diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 034b524594bd..c11b46c33159 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -526,7 +526,7 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp); static void increment_cpu_stall_ticks(void); static int rcu_nocb_needs_gp(struct rcu_state *rsp); static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq); -static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp); +static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp); static void rcu_init_one_nocb(struct rcu_node *rnp); static bool is_nocb_cpu(int cpu); static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index f3f0020b5b58..723af5f707f0 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2022,22 +2022,12 @@ static int rcu_nocb_needs_gp(struct rcu_state *rsp) } /* - * Clean up this rcu_node structure's no-CBs state at the end of - * a grace period, and also return whether any no-CBs CPU associated - * with this rcu_node structure needs another grace period. + * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended + * grace period. */ -static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) +static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) { - int c = rnp->completed; - int needmore; - - wake_up_all(&rnp->nocb_gp_wq[c & 0x1]); - rnp->need_future_gp[c & 0x1] = 0; - needmore = rnp->need_future_gp[(c + 1) & 0x1]; - trace_rcu_future_grace_period(rsp->name, rnp->gpnum, rnp->completed, - c, rnp->level, rnp->grplo, rnp->grphi, - needmore ? "CleanupMore" : "Cleanup"); - return needmore; + wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]); } /* @@ -2175,84 +2165,16 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp) bool d; unsigned long flags; struct rcu_node *rnp = rdp->mynode; - struct rcu_node *rnp_root = rcu_get_root(rdp->rsp); raw_spin_lock_irqsave(&rnp->lock, flags); - c = rnp->completed + 2; - - /* Count our request for a grace period. */ - rnp->need_future_gp[c & 0x1]++; - trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum, - rnp->completed, c, rnp->level, - rnp->grplo, rnp->grphi, "Startleaf"); - - if (rnp->gpnum != rnp->completed) { - - /* - * This rcu_node structure believes that a grace period - * is in progress, so we are done. When this grace - * period ends, our request will be acted upon. - */ - trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum, - rnp->completed, c, rnp->level, - rnp->grplo, rnp->grphi, - "Startedleaf"); - raw_spin_unlock_irqrestore(&rnp->lock, flags); - - } else { - - /* - * Might not be a grace period, check root rcu_node - * structure to see if we must start one. - */ - if (rnp != rnp_root) - raw_spin_lock(&rnp_root->lock); /* irqs disabled. */ - if (rnp_root->gpnum != rnp_root->completed) { - trace_rcu_future_grace_period(rdp->rsp->name, - rnp->gpnum, - rnp->completed, - c, rnp->level, - rnp->grplo, rnp->grphi, - "Startedleafroot"); - raw_spin_unlock(&rnp_root->lock); /* irqs disabled. */ - } else { - - /* - * No grace period, so we need to start one. - * The good news is that we can wait for exactly - * one grace period instead of part of the current - * grace period and all of the next grace period. - * Adjust counters accordingly and start the - * needed grace period. - */ - rnp->need_future_gp[c & 0x1]--; - c = rnp_root->completed + 1; - rnp->need_future_gp[c & 0x1]++; - rnp_root->need_future_gp[c & 0x1]++; - trace_rcu_future_grace_period(rdp->rsp->name, - rnp->gpnum, - rnp->completed, - c, rnp->level, - rnp->grplo, rnp->grphi, - "Startedroot"); - rcu_start_gp(rdp->rsp); - raw_spin_unlock(&rnp->lock); - } - - /* Clean up locking and irq state. */ - if (rnp != rnp_root) - raw_spin_unlock_irqrestore(&rnp->lock, flags); - else - local_irq_restore(flags); - } + c = rcu_start_future_gp(rnp, rdp); + raw_spin_unlock_irqrestore(&rnp->lock, flags); /* * Wait for the grace period. Do so interruptibly to avoid messing * up the load average. */ - trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum, - rnp->completed, c, rnp->level, - rnp->grplo, rnp->grphi, "StartWait"); + trace_rcu_future_gp(rnp, rdp, c, "StartWait"); for (;;) { wait_event_interruptible( rnp->nocb_gp_wq[c & 0x1], @@ -2260,14 +2182,9 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp) if (likely(d)) break; flush_signals(current); - trace_rcu_future_grace_period(rdp->rsp->name, - rnp->gpnum, rnp->completed, c, - rnp->level, rnp->grplo, - rnp->grphi, "ResumeWait"); + trace_rcu_future_gp(rnp, rdp, c, "ResumeWait"); } - trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum, - rnp->completed, c, rnp->level, - rnp->grplo, rnp->grphi, "EndWait"); + trace_rcu_future_gp(rnp, rdp, c, "EndWait"); smp_mb(); /* Ensure that CB invocation happens after GP end. */ } @@ -2375,9 +2292,8 @@ static int rcu_nocb_needs_gp(struct rcu_state *rsp) return 0; } -static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) +static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) { - return 0; } static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) -- cgit v1.2.3 From 910ee45db2f4837c8440e770474758493ab94bf7 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 31 Dec 2012 02:24:21 -0800 Subject: rcu: Make rcu_accelerate_cbs() note need for future grace periods Now that rcu_start_future_gp() has been abstracted from rcu_nocb_wait_gp(), rcu_accelerate_cbs() can invoke rcu_start_future_gp() so as to register the need for any future grace periods needed by a CPU about to enter dyntick-idle mode. This commit makes this change. Note that some refactoring of rcu_start_gp() is carried out to avoid recursion and subsequent self-deadlocks. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 50 ++++++++++++++++++++++++++++++++------------------ 1 file changed, 32 insertions(+), 18 deletions(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f4b23f16677a..9cb91e4885af 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -224,7 +224,8 @@ static ulong jiffies_till_next_fqs = RCU_JIFFIES_TILL_FORCE_QS; module_param(jiffies_till_first_fqs, ulong, 0644); module_param(jiffies_till_next_fqs, ulong, 0644); -static void rcu_start_gp(struct rcu_state *rsp); +static void rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp, + struct rcu_data *rdp); static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)); static void force_quiescent_state(struct rcu_state *rsp); static int rcu_pending(int cpu); @@ -1162,7 +1163,7 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp) trace_rcu_future_gp(rnp, rdp, c, "Startedleafroot"); } else { trace_rcu_future_gp(rnp, rdp, c, "Startedroot"); - rcu_start_gp(rdp->rsp); + rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp); } unlock_out: if (rnp != rnp_root) @@ -1248,6 +1249,8 @@ static void rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp, rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL]; rdp->nxtcompleted[i] = c; } + /* Record any needed additional grace periods. */ + rcu_start_future_gp(rnp, rdp); /* Trace depending on how much we were able to accelerate. */ if (!*rdp->nxttail[RCU_WAIT_TAIL]) @@ -1609,20 +1612,9 @@ static int __noreturn rcu_gp_kthread(void *arg) * quiescent state. */ static void -rcu_start_gp(struct rcu_state *rsp) +rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp, + struct rcu_data *rdp) { - struct rcu_data *rdp = this_cpu_ptr(rsp->rda); - struct rcu_node *rnp = rcu_get_root(rsp); - - /* - * If there is no grace period in progress right now, any - * callbacks we have up to this point will be satisfied by the - * next grace period. Also, advancing the callbacks reduces the - * probability of false positives from cpu_needs_another_gp() - * resulting in pointless grace periods. So, advance callbacks! - */ - rcu_advance_cbs(rsp, rnp, rdp); - if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) { /* * Either we have not yet spawned the grace-period @@ -1634,13 +1626,35 @@ rcu_start_gp(struct rcu_state *rsp) } rsp->gp_flags = RCU_GP_FLAG_INIT; - /* Ensure that CPU is aware of completion of last grace period. */ - __rcu_process_gp_end(rsp, rdp->mynode, rdp); - /* Wake up rcu_gp_kthread() to start the grace period. */ wake_up(&rsp->gp_wq); } +/* + * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's + * callbacks. Note that rcu_start_gp_advanced() cannot do this because it + * is invoked indirectly from rcu_advance_cbs(), which would result in + * endless recursion -- or would do so if it wasn't for the self-deadlock + * that is encountered beforehand. + */ +static void +rcu_start_gp(struct rcu_state *rsp) +{ + struct rcu_data *rdp = this_cpu_ptr(rsp->rda); + struct rcu_node *rnp = rcu_get_root(rsp); + + /* + * If there is no grace period in progress right now, any + * callbacks we have up to this point will be satisfied by the + * next grace period. Also, advancing the callbacks reduces the + * probability of false positives from cpu_needs_another_gp() + * resulting in pointless grace periods. So, advance callbacks + * then start the grace period! + */ + rcu_advance_cbs(rsp, rnp, rdp); + rcu_start_gp_advanced(rsp, rnp, rdp); +} + /* * Report a full set of quiescent states to the specified rcu_state * data structure. This involves cleaning up after the prior grace -- cgit v1.2.3