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perf/core: Document some hotplug bits

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Document some of the hotplug notifier usage.

Requested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2016-03-08 17:56:05 +01:00 • committed by Ingo Molnar
parent f8519155b4
commit 1dcaac1ce0
1 changed files with 19 additions and 0 deletions
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19
kernel/events/core.c
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@ -9449,10 +9449,29 @@ perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu)
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_UP_PREPARE:
/*
* This must be done before the CPU comes alive, because the
* moment we can run tasks we can encounter (software) events.
*
* Specifically, someone can have inherited events on kthreadd
* or a pre-existing worker thread that gets re-bound.
*/
perf_event_init_cpu(cpu);
break;
case CPU_DOWN_PREPARE:
/*
* This must be done before the CPU dies because after that an
* active event might want to IPI the CPU and that'll not work
* so great for dead CPUs.
*
* XXX smp_call_function_single() return -ENXIO without a warn
* so we could possibly deal with this.
*
* This is safe against new events arriving because
* sys_perf_event_open() serializes against hotplug using
* get_online_cpus().
*/
perf_event_exit_cpu(cpu);
break;
default: