diff options
| -rw-r--r-- | Documentation/RCU/trace.txt | 36 | ||||
| -rw-r--r-- | kernel/rcu/tree.c | 16 | ||||
| -rw-r--r-- | kernel/rcu/tree.h | 2 | ||||
| -rw-r--r-- | kernel/rcu/tree_trace.c | 4 |
4 files changed, 29 insertions, 29 deletions
diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt index 08651da15448..97f17e9decda 100644 --- a/Documentation/RCU/trace.txt +++ b/Documentation/RCU/trace.txt @@ -237,42 +237,26 @@ o "ktl" is the low-order 16 bits (in hexadecimal) of the count of The output of "cat rcu/rcu_preempt/rcuexp" looks as follows: -s=21872 d=21872 w=0 tf=0 wd1=0 wd2=0 n=0 sc=21872 dt=21872 dl=0 dx=21872 +s=21872 wd0=0 wd1=0 wd2=0 wd3=5 n=0 enq=0 sc=21872 These fields are as follows: -o "s" is the starting sequence number. +o "s" is the sequence number, with an odd number indicating that + an expedited grace period is in progress. -o "d" is the ending sequence number. When the starting and ending - numbers differ, there is an expedited grace period in progress. - -o "w" is the number of times that the sequence numbers have been - in danger of wrapping. - -o "tf" is the number of times that contention has resulted in a - failure to begin an expedited grace period. - -o "wd1" and "wd2" are the number of times that an attempt to - start an expedited grace period found that someone else had - completed an expedited grace period that satisfies the +o "wd0", "wd1", "wd2", and "wd3" are the number of times that an + attempt to start an expedited grace period found that someone + else had completed an expedited grace period that satisfies the attempted request. "Our work is done." -o "n" is number of times that contention was so great that - the request was demoted from an expedited grace period to - a normal grace period. +o "n" is number of times that a concurrent CPU-hotplug operation + forced a fallback to a normal grace period. + +o "enq" is the number of quiescent states still outstanding. o "sc" is the number of times that the attempt to start a new expedited grace period succeeded. -o "dt" is the number of times that we attempted to update - the "d" counter. - -o "dl" is the number of times that we failed to update the "d" - counter. - -o "dx" is the number of times that we succeeded in updating - the "d" counter. - The output of "cat rcu/rcu_preempt/rcugp" looks as follows: diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f66f6e7730bc..3af0dee2d045 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3356,6 +3356,22 @@ static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s) struct rcu_node *rnp1 = NULL; /* + * First try directly acquiring the root lock in order to reduce + * latency in the common case where expedited grace periods are + * rare. We check mutex_is_locked() to avoid pathological levels of + * memory contention on ->exp_funnel_mutex in the heavy-load case. + */ + rnp0 = rcu_get_root(rsp); + if (!mutex_is_locked(&rnp0->exp_funnel_mutex)) { + if (mutex_trylock(&rnp0->exp_funnel_mutex)) { + if (sync_exp_work_done(rsp, rnp0, NULL, + &rsp->expedited_workdone0, s)) + return NULL; + return rnp0; + } + } + + /* * Each pass through the following loop works its way * up the rcu_node tree, returning if others have done the * work or otherwise falls through holding the root rnp's diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 543ba726396c..80d974df0ea0 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -493,7 +493,7 @@ struct rcu_state { /* End of fields guarded by barrier_mutex. */ unsigned long expedited_sequence; /* Take a ticket. */ - atomic_long_t expedited_tryfail; /* # acquisition failures. */ + atomic_long_t expedited_workdone0; /* # done by others #0. */ atomic_long_t expedited_workdone1; /* # done by others #1. */ atomic_long_t expedited_workdone2; /* # done by others #2. */ atomic_long_t expedited_workdone3; /* # done by others #3. */ diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c index ec62369f1b02..6fc4c5ff3bb5 100644 --- a/kernel/rcu/tree_trace.c +++ b/kernel/rcu/tree_trace.c @@ -185,9 +185,9 @@ static int show_rcuexp(struct seq_file *m, void *v) { struct rcu_state *rsp = (struct rcu_state *)m->private; - seq_printf(m, "t=%lu tf=%lu wd1=%lu wd2=%lu wd3=%lu n=%lu enq=%d sc=%lu\n", + seq_printf(m, "s=%lu wd0=%lu wd1=%lu wd2=%lu wd3=%lu n=%lu enq=%d sc=%lu\n", rsp->expedited_sequence, - atomic_long_read(&rsp->expedited_tryfail), + atomic_long_read(&rsp->expedited_workdone0), atomic_long_read(&rsp->expedited_workdone1), atomic_long_read(&rsp->expedited_workdone2), atomic_long_read(&rsp->expedited_workdone3), |