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Commit a486143d authored by Raghavendra Rao Ananta's avatar Raghavendra Rao Ananta Committed by Mukesh Ojha
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perf: Cancel the mux hrtimer during CPU hotplug to avoid migration 



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: default avatarRaghavendra Rao Ananta <rananta@codeaurora.org>
[mojha@codeaurora.org: Resolved merge conflict and added missing
 `cpuctx` variable to avoid build failure]
Signed-off-by: default avatarMukesh Ojha <mojha@codeaurora.org>
parent 982f5648

include/linux/perf_event.h

+1 −1
Original line number Diff line number Diff line
@@ -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;

kernel/events/core.c

+14 −1
Original line number Diff line number Diff line
@@ -9656,13 +9656,26 @@ 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