Commit 3cbaa590 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf: Fix ctx time tracking by introducing EVENT_TIME 



Currently any ctx_sched_in() call will re-start the ctx time tracking,
this means that calls like:

	ctx_sched_in(.event_type = EVENT_PINNED);
	ctx_sched_in(.event_type = EVENT_FLEXIBLE);

will have a hole in their ctx time tracking. This is likely harmless
but can confuse things a little. By adding EVENT_TIME, we can have the
first ctx_sched_in() (is_active: 0 -> !0) start the time and any
further ctx_sched_in() will leave the timestamps alone.

Secondly, this allows for an early disable like:

	ctx_sched_out(.event_type = EVENT_TIME);

which would update the ctx time (if the ctx is active) and any further
calls to ctx_sched_out() would not further modify the ctx time.

For ctx_sched_in() any 0 -> !0 transition will automatically include
EVENT_TIME.

For ctx_sched_out(), any transition that clears EVENT_ALL will
automatically clear EVENT_TIME.

These two rules ensure that under normal circumstances we need not
bother with EVENT_TIME and get natural ctx time behaviour.

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: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dvyukov@google.com
Cc: eranian@google.com
Cc: oleg@redhat.com
Cc: panand@redhat.com
Cc: sasha.levin@oracle.com
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/20160224174948.100446561@infradead.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 28a967c3

kernel/events/core.c

+30 −12
Original line number Diff line number Diff line
@@ -314,6 +314,7 @@ again: 
enum event_type_t {

	EVENT_FLEXIBLE = 0x1,

	EVENT_PINNED = 0x2,

	EVENT_TIME = 0x4,

	EVENT_ALL = EVENT_FLEXIBLE | EVENT_PINNED,

};
@@ -1294,16 +1295,18 @@ static u64 perf_event_time(struct perf_event *event) 


/*

 * Update the total_time_enabled and total_time_running fields for a event.

 * The caller of this function needs to hold the ctx->lock.

 */

static void update_event_times(struct perf_event *event)

{

	struct perf_event_context *ctx = event->ctx;

	u64 run_end;



	lockdep_assert_held(&ctx->lock);



	if (event->state < PERF_EVENT_STATE_INACTIVE ||

	    event->group_leader->state < PERF_EVENT_STATE_INACTIVE)

		return;



	/*

	 * in cgroup mode, time_enabled represents

	 * the time the event was enabled AND active
@@ -2349,24 +2352,33 @@ static void ctx_sched_out(struct perf_event_context *ctx, 
	}



	ctx->is_active &= ~event_type;

	if (!(ctx->is_active & EVENT_ALL))

		ctx->is_active = 0;



	if (ctx->task) {

		WARN_ON_ONCE(cpuctx->task_ctx != ctx);

		if (!ctx->is_active)

			cpuctx->task_ctx = NULL;

	}



	is_active ^= ctx->is_active; /* changed bits */



	if (is_active & EVENT_TIME) {

		/* update (and stop) ctx time */

		update_context_time(ctx);

		update_cgrp_time_from_cpuctx(cpuctx);

	if (!ctx->nr_active)

	}



	if (!ctx->nr_active || !(is_active & EVENT_ALL))

		return;



	perf_pmu_disable(ctx->pmu);

	if ((is_active & EVENT_PINNED) && (event_type & EVENT_PINNED)) {

	if (is_active & EVENT_PINNED) {

		list_for_each_entry(event, &ctx->pinned_groups, group_entry)

			group_sched_out(event, cpuctx, ctx);

	}



	if ((is_active & EVENT_FLEXIBLE) && (event_type & EVENT_FLEXIBLE)) {

	if (is_active & EVENT_FLEXIBLE) {

		list_for_each_entry(event, &ctx->flexible_groups, group_entry)

			group_sched_out(event, cpuctx, ctx);

	}
@@ -2740,7 +2752,7 @@ ctx_sched_in(struct perf_event_context *ctx, 
	if (likely(!ctx->nr_events))

		return;



	ctx->is_active |= event_type;

	ctx->is_active |= (event_type | EVENT_TIME);

	if (ctx->task) {

		if (!is_active)

			cpuctx->task_ctx = ctx;
@@ -2748,18 +2760,24 @@ ctx_sched_in(struct perf_event_context *ctx, 
			WARN_ON_ONCE(cpuctx->task_ctx != ctx);

	}



	is_active ^= ctx->is_active; /* changed bits */



	if (is_active & EVENT_TIME) {

		/* start ctx time */

		now = perf_clock();

		ctx->timestamp = now;

		perf_cgroup_set_timestamp(task, ctx);

	}



	/*

	 * First go through the list and put on any pinned groups

	 * in order to give them the best chance of going on.

	 */

	if (!(is_active & EVENT_PINNED) && (event_type & EVENT_PINNED))

	if (is_active & EVENT_PINNED)

		ctx_pinned_sched_in(ctx, cpuctx);



	/* Then walk through the lower prio flexible groups */

	if (!(is_active & EVENT_FLEXIBLE) && (event_type & EVENT_FLEXIBLE))

	if (is_active & EVENT_FLEXIBLE)

		ctx_flexible_sched_in(ctx, cpuctx);

}

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