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: Peter 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: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index de14b67a3b0bcfc0fe5b80320a620a9951ec1674..75bde93eb76fe73bf3a0ce3237198eacbad782b6 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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;
        }
 
-       update_context_time(ctx);
-       update_cgrp_time_from_cpuctx(cpuctx);
-       if (!ctx->nr_active)
+       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 || !(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);
        }
 
-       now = perf_clock();
-       ctx->timestamp = now;
-       perf_cgroup_set_timestamp(task, 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);
 }