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perf: Cancel the mux hrtimer during CPU hotplug to avoid migration

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The current design of hrtimers migrates the pinned timers to a
different CPU upon its hotplug. However, perf-core needs to
maintain the mux-hrtimers on a per CPU basis. That is, each
hrtimer carries the context for that particular CPU and would
lose this context if it gets migrated to a different CPU. As a
result, cancel the hrtimer for the CPU that's about to go down
and restart it (if required) when the perf-events are being created.

Change-Id: I7a1d0456208855e3a99a7d49e59c6dae811d146e
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>
[mojha@codeaurora.org: Resolved merge conflict and added missing
 `cpuctx` variable to avoid build failure]
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>
This commit is contained in:
Raghavendra Rao Ananta 2018-10-19 10:06:28 -07:00 • committed by Gerrit - the friendly Code Review server
parent b55c37ac6f
commit ea2ee83c92
2 changed files with 15 additions and 2 deletions
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2
include/linux/perf_event.h
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@ -231,7 +231,7 @@ struct pmu {
int capabilities;
int * __percpu pmu_disable_count;
struct perf_cpu_context * __percpu pmu_cpu_context;
struct perf_cpu_context __percpu *pmu_cpu_context;
atomic_t exclusive_cnt; /* < 0: cpu; > 0: tsk */
int task_ctx_nr;
int hrtimer_interval_ms;

15
kernel/events/core.c
View file

@ -9654,13 +9654,26 @@ static void __perf_event_stop_swclock(void *__info)
static void perf_event_exit_cpu_context(int cpu)
{
struct perf_cpu_context *cpuctx;
struct perf_event_context *ctx;
unsigned long flags;
struct pmu *pmu;
int idx;
idx = srcu_read_lock(&pmus_srcu);
list_for_each_entry_rcu(pmu, &pmus, entry) {
ctx = &per_cpu_ptr(pmu->pmu_cpu_context, cpu)->ctx;
cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
ctx = &cpuctx->ctx;
/* Cancel the mux hrtimer to avoid CPU migration */
if (pmu->task_ctx_nr != perf_sw_context) {
raw_spin_lock_irqsave(&cpuctx->hrtimer_lock, flags);
hrtimer_cancel(&cpuctx->hrtimer);
cpuctx->hrtimer_active = 0;
raw_spin_unlock_irqrestore(&cpuctx->hrtimer_lock,
flags);
}
mutex_lock(&ctx->mutex);
/*
* If keeping events across hotplugging is supported, do not