[tip:perf/core] perf/core: Don't re-schedule CPU flexible events needlessly

[tip-bot for Alexander Shishkin <tipbot@zytor.com>]

Commit-ID:  fe45bafbd0e1b5e828aa9d44d07e569df85869a2
Gitweb:     http://git.kernel.org/tip/fe45bafbd0e1b5e828aa9d44d07e569df85869a2
Author:     Alexander Shishkin <alexander.shishkin@linux.intel.com>
AuthorDate: Thu, 19 Jan 2017 18:43:29 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 30 Jan 2017 12:01:14 +0100

perf/core: Don't re-schedule CPU flexible events needlessly

In the sched-in path, we first remove a CPU's flexible events in order to
give priority to the task's pinned events. However, this step can be safely
skipped if the task doesn't have its own pinned events.

This patch implements this skipping.

Reported-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
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: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/20170119164330.22887-2-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/events/core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index d92c7ad..8c0b733 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3122,8 +3122,12 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
 	 * We want to keep the following priority order:
 	 * cpu pinned (that don't need to move), task pinned,
 	 * cpu flexible, task flexible.
+	 *
+	 * However, if task's ctx is not carrying any pinned
+	 * events, no need to flip the cpuctx's events around.
 	 */
-	cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
+	if (!list_empty(&ctx->pinned_groups))
+		cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
 	perf_event_sched_in(cpuctx, ctx, task);
 	perf_pmu_enable(ctx->pmu);
 	perf_ctx_unlock(cpuctx, ctx);