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Commit 8d5bce0c authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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perf/core: Optimize perf_rotate_context() event scheduling 



The event schedule order (as per perf_event_sched_in()) is:

 - cpu  pinned
 - task pinned
 - cpu  flexible
 - task flexible

But perf_rotate_context() will unschedule cpu-flexible even if it
doesn't need a rotation.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 8703a7cf

kernel/events/core.c

+37 −23
Original line number Diff line number Diff line
@@ -430,7 +430,7 @@ static void update_perf_cpu_limits(void) 
	WRITE_ONCE(perf_sample_allowed_ns, tmp);

}



static int perf_rotate_context(struct perf_cpu_context *cpuctx);

static bool perf_rotate_context(struct perf_cpu_context *cpuctx);



int perf_proc_update_handler(struct ctl_table *table, int write,

		void __user *buffer, size_t *lenp,
@@ -1041,7 +1041,7 @@ list_update_cgroup_event(struct perf_event *event, 
static enum hrtimer_restart perf_mux_hrtimer_handler(struct hrtimer *hr)

{

	struct perf_cpu_context *cpuctx;

	int rotations = 0;

	bool rotations;



	lockdep_assert_irqs_disabled();
@@ -3600,52 +3600,66 @@ static void rotate_ctx(struct perf_event_context *ctx, struct perf_event *event) 
	perf_event_groups_insert(&ctx->flexible_groups, event);

}



static int perf_rotate_context(struct perf_cpu_context *cpuctx)

static inline struct perf_event *

ctx_first_active(struct perf_event_context *ctx)

{

	struct perf_event *ctx_event = NULL, *cpuctx_event = NULL;

	return list_first_entry_or_null(&ctx->flexible_active,

					struct perf_event, active_list);

}



static bool perf_rotate_context(struct perf_cpu_context *cpuctx)

{

	struct perf_event *cpu_event = NULL, *task_event = NULL;

	bool cpu_rotate = false, task_rotate = false;

	struct perf_event_context *ctx = NULL;

	int rotate = 0;



	/*

	 * Since we run this from IRQ context, nobody can install new

	 * events, thus the event count values are stable.

	 */



	if (cpuctx->ctx.nr_events) {

		if (cpuctx->ctx.nr_events != cpuctx->ctx.nr_active)

			rotate = 1;

			cpu_rotate = true;

	}



	ctx = cpuctx->task_ctx;

	if (ctx && ctx->nr_events) {

		if (ctx->nr_events != ctx->nr_active)

			rotate = 1;

			task_rotate = true;

	}



	if (!rotate)

		goto done;

	if (!(cpu_rotate || task_rotate))

		return false;



	perf_ctx_lock(cpuctx, cpuctx->task_ctx);

	perf_pmu_disable(cpuctx->ctx.pmu);



	cpuctx_event = list_first_entry_or_null(&cpuctx->ctx.flexible_active,

						struct perf_event, active_list);

	if (ctx) {

		ctx_event = list_first_entry_or_null(&ctx->flexible_active,

						     struct perf_event, active_list);

	}

	if (task_rotate)

		task_event = ctx_first_active(ctx);

	if (cpu_rotate)

		cpu_event = ctx_first_active(&cpuctx->ctx);



	cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);

	if (ctx)

	/*

	 * As per the order given at ctx_resched() first 'pop' task flexible

	 * and then, if needed CPU flexible.

	 */

	if (task_event || (ctx && cpu_event))

		ctx_sched_out(ctx, cpuctx, EVENT_FLEXIBLE);

	if (cpu_event)

		cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);



	if (cpuctx_event)

		rotate_ctx(&cpuctx->ctx, cpuctx_event);

	if (ctx_event)

		rotate_ctx(ctx, ctx_event);

	if (task_event)

		rotate_ctx(ctx, task_event);

	if (cpu_event)

		rotate_ctx(&cpuctx->ctx, cpu_event);



	perf_event_sched_in(cpuctx, ctx, current);



	perf_pmu_enable(cpuctx->ctx.pmu);

	perf_ctx_unlock(cpuctx, cpuctx->task_ctx);

done:



	return rotate;

	return true;

}



void perf_event_task_tick(void)