diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2016-03-15 13:50:29 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-03-15 13:50:29 -0700 |
commit | 710d60cbf1b312a8075a2158cbfbbd9c66132dcc (patch) | |
tree | d46a9f1a14165807701f1868398a6dc76af85968 /include | |
parent | df2e37c814d51692803245fcbecca360d4882e96 (diff) | |
parent | d10ef6f9380b8853c4b48eb104268fccfdc0b0c5 (diff) |
Merge branch 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull cpu hotplug updates from Thomas Gleixner:
"This is the first part of the ongoing cpu hotplug rework:
- Initial implementation of the state machine
- Runs all online and prepare down callbacks on the plugged cpu and
not on some random processor
- Replaces busy loop waiting with completions
- Adds tracepoints so the states can be followed"
More detailed commentary on this work from an earlier email:
"What's wrong with the current cpu hotplug infrastructure?
- Asymmetry
The hotplug notifier mechanism is asymmetric versus the bringup and
teardown. This is mostly caused by the notifier mechanism.
- Largely undocumented dependencies
While some notifiers use explicitely defined notifier priorities,
we have quite some notifiers which use numerical priorities to
express dependencies without any documentation why.
- Control processor driven
Most of the bringup/teardown of a cpu is driven by a control
processor. While it is understandable, that preperatory steps,
like idle thread creation, memory allocation for and initialization
of essential facilities needs to be done before a cpu can boot,
there is no reason why everything else must run on a control
processor. Before this patch series, bringup looks like this:
Control CPU Booting CPU
do preparatory steps
kick cpu into life
do low level init
sync with booting cpu sync with control cpu
bring the rest up
- All or nothing approach
There is no way to do partial bringups. That's something which is
really desired because we waste e.g. at boot substantial amount of
time just busy waiting that the cpu comes to life. That's stupid
as we could very well do preparatory steps and the initial IPI for
other cpus and then go back and do the necessary low level
synchronization with the freshly booted cpu.
- Minimal debuggability
Due to the notifier based design, it's impossible to switch between
two stages of the bringup/teardown back and forth in order to test
the correctness. So in many hotplug notifiers the cancel
mechanisms are either not existant or completely untested.
- Notifier [un]registering is tedious
To [un]register notifiers we need to protect against hotplug at
every callsite. There is no mechanism that bringup/teardown
callbacks are issued on the online cpus, so every caller needs to
do it itself. That also includes error rollback.
What's the new design?
The base of the new design is a symmetric state machine, where both
the control processor and the booting/dying cpu execute a well
defined set of states. Each state is symmetric in the end, except
for some well defined exceptions, and the bringup/teardown can be
stopped and reversed at almost all states.
So the bringup of a cpu will look like this in the future:
Control CPU Booting CPU
do preparatory steps
kick cpu into life
do low level init
sync with booting cpu sync with control cpu
bring itself up
The synchronization step does not require the control cpu to wait.
That mechanism can be done asynchronously via a worker or some
other mechanism.
The teardown can be made very similar, so that the dying cpu cleans
up and brings itself down. Cleanups which need to be done after
the cpu is gone, can be scheduled asynchronously as well.
There is a long way to this, as we need to refactor the notion when a
cpu is available. Today we set the cpu online right after it comes
out of the low level bringup, which is not really correct.
The proper mechanism is to set it to available, i.e. cpu local
threads, like softirqd, hotplug thread etc. can be scheduled on that
cpu, and once it finished all booting steps, it's set to online, so
general workloads can be scheduled on it. The reverse happens on
teardown. First thing to do is to forbid scheduling of general
workloads, then teardown all the per cpu resources and finally shut it
off completely.
This patch series implements the basic infrastructure for this at the
core level. This includes the following:
- Basic state machine implementation with well defined states, so
ordering and prioritization can be expressed.
- Interfaces to [un]register state callbacks
This invokes the bringup/teardown callback on all online cpus with
the proper protection in place and [un]installs the callbacks in
the state machine array.
For callbacks which have no particular ordering requirement we have
a dynamic state space, so that drivers don't have to register an
explicit hotplug state.
If a callback fails, the code automatically does a rollback to the
previous state.
- Sysfs interface to drive the state machine to a particular step.
This is only partially functional today. Full functionality and
therefor testability will be achieved once we converted all
existing hotplug notifiers over to the new scheme.
- Run all CPU_ONLINE/DOWN_PREPARE notifiers on the booting/dying
processor:
Control CPU Booting CPU
do preparatory steps
kick cpu into life
do low level init
sync with booting cpu sync with control cpu
wait for boot
bring itself up
Signal completion to control cpu
In a previous step of this work we've done a full tree mechanical
conversion of all hotplug notifiers to the new scheme. The balance
is a net removal of about 4000 lines of code.
This is not included in this series, as we decided to take a
different approach. Instead of mechanically converting everything
over, we will do a proper overhaul of the usage sites one by one so
they nicely fit into the symmetric callback scheme.
I decided to do that after I looked at the ugliness of some of the
converted sites and figured out that their hotplug mechanism is
completely buggered anyway. So there is no point to do a
mechanical conversion first as we need to go through the usage
sites one by one again in order to achieve a full symmetric and
testable behaviour"
* 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (23 commits)
cpu/hotplug: Document states better
cpu/hotplug: Fix smpboot thread ordering
cpu/hotplug: Remove redundant state check
cpu/hotplug: Plug death reporting race
rcu: Make CPU_DYING_IDLE an explicit call
cpu/hotplug: Make wait for dead cpu completion based
cpu/hotplug: Let upcoming cpu bring itself fully up
arch/hotplug: Call into idle with a proper state
cpu/hotplug: Move online calls to hotplugged cpu
cpu/hotplug: Create hotplug threads
cpu/hotplug: Split out the state walk into functions
cpu/hotplug: Unpark smpboot threads from the state machine
cpu/hotplug: Move scheduler cpu_online notifier to hotplug core
cpu/hotplug: Implement setup/removal interface
cpu/hotplug: Make target state writeable
cpu/hotplug: Add sysfs state interface
cpu/hotplug: Hand in target state to _cpu_up/down
cpu/hotplug: Convert the hotplugged cpu work to a state machine
cpu/hotplug: Convert to a state machine for the control processor
cpu/hotplug: Add tracepoints
...
Diffstat (limited to 'include')
-rw-r--r-- | include/linux/cpu.h | 27 | ||||
-rw-r--r-- | include/linux/cpuhotplug.h | 93 | ||||
-rw-r--r-- | include/linux/notifier.h | 2 | ||||
-rw-r--r-- | include/linux/rcupdate.h | 4 | ||||
-rw-r--r-- | include/trace/events/cpuhp.h | 66 |
5 files changed, 173 insertions, 19 deletions
diff --git a/include/linux/cpu.h b/include/linux/cpu.h index d2ca8c38f9c4..f9b1fab4388a 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -16,6 +16,7 @@ #include <linux/node.h> #include <linux/compiler.h> #include <linux/cpumask.h> +#include <linux/cpuhotplug.h> struct device; struct device_node; @@ -27,6 +28,9 @@ struct cpu { struct device dev; }; +extern void boot_cpu_init(void); +extern void boot_cpu_state_init(void); + extern int register_cpu(struct cpu *cpu, int num); extern struct device *get_cpu_device(unsigned cpu); extern bool cpu_is_hotpluggable(unsigned cpu); @@ -74,7 +78,7 @@ enum { /* migration should happen before other stuff but after perf */ CPU_PRI_PERF = 20, CPU_PRI_MIGRATION = 10, - CPU_PRI_SMPBOOT = 9, + /* bring up workqueues before normal notifiers and down after */ CPU_PRI_WORKQUEUE_UP = 5, CPU_PRI_WORKQUEUE_DOWN = -5, @@ -97,9 +101,7 @@ enum { * Called on the new cpu, just before * enabling interrupts. Must not sleep, * must not fail */ -#define CPU_DYING_IDLE 0x000B /* CPU (unsigned)v dying, reached - * idle loop. */ -#define CPU_BROKEN 0x000C /* CPU (unsigned)v did not die properly, +#define CPU_BROKEN 0x000B /* CPU (unsigned)v did not die properly, * perhaps due to preemption. */ /* Used for CPU hotplug events occurring while tasks are frozen due to a suspend @@ -118,6 +120,7 @@ enum { #ifdef CONFIG_SMP +extern bool cpuhp_tasks_frozen; /* Need to know about CPUs going up/down? */ #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) #define cpu_notifier(fn, pri) { \ @@ -167,7 +170,6 @@ static inline void __unregister_cpu_notifier(struct notifier_block *nb) } #endif -void smpboot_thread_init(void); int cpu_up(unsigned int cpu); void notify_cpu_starting(unsigned int cpu); extern void cpu_maps_update_begin(void); @@ -177,6 +179,7 @@ extern void cpu_maps_update_done(void); #define cpu_notifier_register_done cpu_maps_update_done #else /* CONFIG_SMP */ +#define cpuhp_tasks_frozen 0 #define cpu_notifier(fn, pri) do { (void)(fn); } while (0) #define __cpu_notifier(fn, pri) do { (void)(fn); } while (0) @@ -215,10 +218,6 @@ static inline void cpu_notifier_register_done(void) { } -static inline void smpboot_thread_init(void) -{ -} - #endif /* CONFIG_SMP */ extern struct bus_type cpu_subsys; @@ -265,11 +264,6 @@ static inline int disable_nonboot_cpus(void) { return 0; } static inline void enable_nonboot_cpus(void) {} #endif /* !CONFIG_PM_SLEEP_SMP */ -enum cpuhp_state { - CPUHP_OFFLINE, - CPUHP_ONLINE, -}; - void cpu_startup_entry(enum cpuhp_state state); void cpu_idle_poll_ctrl(bool enable); @@ -280,14 +274,15 @@ void arch_cpu_idle_enter(void); void arch_cpu_idle_exit(void); void arch_cpu_idle_dead(void); -DECLARE_PER_CPU(bool, cpu_dead_idle); - int cpu_report_state(int cpu); int cpu_check_up_prepare(int cpu); void cpu_set_state_online(int cpu); #ifdef CONFIG_HOTPLUG_CPU bool cpu_wait_death(unsigned int cpu, int seconds); bool cpu_report_death(void); +void cpuhp_report_idle_dead(void); +#else +static inline void cpuhp_report_idle_dead(void) { } #endif /* #ifdef CONFIG_HOTPLUG_CPU */ #endif /* _LINUX_CPU_H_ */ diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h new file mode 100644 index 000000000000..5d68e15e46b7 --- /dev/null +++ b/include/linux/cpuhotplug.h @@ -0,0 +1,93 @@ +#ifndef __CPUHOTPLUG_H +#define __CPUHOTPLUG_H + +enum cpuhp_state { + CPUHP_OFFLINE, + CPUHP_CREATE_THREADS, + CPUHP_NOTIFY_PREPARE, + CPUHP_BRINGUP_CPU, + CPUHP_AP_IDLE_DEAD, + CPUHP_AP_OFFLINE, + CPUHP_AP_NOTIFY_STARTING, + CPUHP_AP_ONLINE, + CPUHP_TEARDOWN_CPU, + CPUHP_AP_ONLINE_IDLE, + CPUHP_AP_SMPBOOT_THREADS, + CPUHP_AP_NOTIFY_ONLINE, + CPUHP_AP_ONLINE_DYN, + CPUHP_AP_ONLINE_DYN_END = CPUHP_AP_ONLINE_DYN + 30, + CPUHP_ONLINE, +}; + +int __cpuhp_setup_state(enum cpuhp_state state, const char *name, bool invoke, + int (*startup)(unsigned int cpu), + int (*teardown)(unsigned int cpu)); + +/** + * cpuhp_setup_state - Setup hotplug state callbacks with calling the callbacks + * @state: The state for which the calls are installed + * @name: Name of the callback (will be used in debug output) + * @startup: startup callback function + * @teardown: teardown callback function + * + * Installs the callback functions and invokes the startup callback on + * the present cpus which have already reached the @state. + */ +static inline int cpuhp_setup_state(enum cpuhp_state state, + const char *name, + int (*startup)(unsigned int cpu), + int (*teardown)(unsigned int cpu)) +{ + return __cpuhp_setup_state(state, name, true, startup, teardown); +} + +/** + * cpuhp_setup_state_nocalls - Setup hotplug state callbacks without calling the + * callbacks + * @state: The state for which the calls are installed + * @name: Name of the callback. + * @startup: startup callback function + * @teardown: teardown callback function + * + * Same as @cpuhp_setup_state except that no calls are executed are invoked + * during installation of this callback. NOP if SMP=n or HOTPLUG_CPU=n. + */ +static inline int cpuhp_setup_state_nocalls(enum cpuhp_state state, + const char *name, + int (*startup)(unsigned int cpu), + int (*teardown)(unsigned int cpu)) +{ + return __cpuhp_setup_state(state, name, false, startup, teardown); +} + +void __cpuhp_remove_state(enum cpuhp_state state, bool invoke); + +/** + * cpuhp_remove_state - Remove hotplug state callbacks and invoke the teardown + * @state: The state for which the calls are removed + * + * Removes the callback functions and invokes the teardown callback on + * the present cpus which have already reached the @state. + */ +static inline void cpuhp_remove_state(enum cpuhp_state state) +{ + __cpuhp_remove_state(state, true); +} + +/** + * cpuhp_remove_state_nocalls - Remove hotplug state callbacks without invoking + * teardown + * @state: The state for which the calls are removed + */ +static inline void cpuhp_remove_state_nocalls(enum cpuhp_state state) +{ + __cpuhp_remove_state(state, false); +} + +#ifdef CONFIG_SMP +void cpuhp_online_idle(enum cpuhp_state state); +#else +static inline void cpuhp_online_idle(enum cpuhp_state state) { } +#endif + +#endif diff --git a/include/linux/notifier.h b/include/linux/notifier.h index d14a4c362465..4149868de4e6 100644 --- a/include/linux/notifier.h +++ b/include/linux/notifier.h @@ -47,6 +47,8 @@ * runtime initialization. */ +struct notifier_block; + typedef int (*notifier_fn_t)(struct notifier_block *nb, unsigned long action, void *data); diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index b5d48bd56e3f..2657aff2725b 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -332,9 +332,7 @@ void rcu_init(void); void rcu_sched_qs(void); void rcu_bh_qs(void); void rcu_check_callbacks(int user); -struct notifier_block; -int rcu_cpu_notify(struct notifier_block *self, - unsigned long action, void *hcpu); +void rcu_report_dead(unsigned int cpu); #ifndef CONFIG_TINY_RCU void rcu_end_inkernel_boot(void); diff --git a/include/trace/events/cpuhp.h b/include/trace/events/cpuhp.h new file mode 100644 index 000000000000..a72bd93ec7e5 --- /dev/null +++ b/include/trace/events/cpuhp.h @@ -0,0 +1,66 @@ +#undef TRACE_SYSTEM +#define TRACE_SYSTEM cpuhp + +#if !defined(_TRACE_CPUHP_H) || defined(TRACE_HEADER_MULTI_READ) +#define _TRACE_CPUHP_H + +#include <linux/tracepoint.h> + +TRACE_EVENT(cpuhp_enter, + + TP_PROTO(unsigned int cpu, + int target, + int idx, + int (*fun)(unsigned int)), + + TP_ARGS(cpu, target, idx, fun), + + TP_STRUCT__entry( + __field( unsigned int, cpu ) + __field( int, target ) + __field( int, idx ) + __field( void *, fun ) + ), + + TP_fast_assign( + __entry->cpu = cpu; + __entry->target = target; + __entry->idx = idx; + __entry->fun = fun; + ), + + TP_printk("cpu: %04u target: %3d step: %3d (%pf)", + __entry->cpu, __entry->target, __entry->idx, __entry->fun) +); + +TRACE_EVENT(cpuhp_exit, + + TP_PROTO(unsigned int cpu, + int state, + int idx, + int ret), + + TP_ARGS(cpu, state, idx, ret), + + TP_STRUCT__entry( + __field( unsigned int, cpu ) + __field( int, state ) + __field( int, idx ) + __field( int, ret ) + ), + + TP_fast_assign( + __entry->cpu = cpu; + __entry->state = state; + __entry->idx = idx; + __entry->ret = ret; + ), + + TP_printk(" cpu: %04u state: %3d step: %3d ret: %d", + __entry->cpu, __entry->state, __entry->idx, __entry->ret) +); + +#endif + +/* This part must be outside protection */ +#include <trace/define_trace.h> |