perf/core: Optimize perf_pmu_sched_task()
authorPeter Zijlstra <peterz@infradead.org>
Wed, 6 Jul 2016 07:18:30 +0000 (09:18 +0200)
committerIngo Molnar <mingo@kernel.org>
Wed, 10 Aug 2016 11:13:28 +0000 (13:13 +0200)
commite48c178814b4a33f84f62d01f5a601ebd57fbba8
treeb4ea583e868d79b8bc9140007703db2d9634da6c
parent3e2c1a67d616dbc1034bc39448cd5f4aa3bd3cca
perf/core: Optimize perf_pmu_sched_task()

For perf record -b, which requires the pmu::sched_task callback the
current code is rather expensive:

     7.68%  sched-pipe  [kernel.vmlinux]    [k] perf_pmu_sched_task
     5.95%  sched-pipe  [kernel.vmlinux]    [k] __switch_to
     5.20%  sched-pipe  [kernel.vmlinux]    [k] __intel_pmu_disable_all
     3.95%  sched-pipe  perf                [.] worker_thread

The problem is that it will iterate all registered PMUs, most of which
will not have anything to do. Avoid this by keeping an explicit list
of PMUs that have requested the callback.

The perf_sched_cb_{inc,dec}() functions already takes the required pmu
argument, and now that these functions are no longer called from NMI
context we can use them to manage a list.

With this patch applied the function doesn't show up in the top 4
anymore (it dropped to 18th place).

     6.67%  sched-pipe  [kernel.vmlinux]    [k] __switch_to
     6.18%  sched-pipe  [kernel.vmlinux]    [k] __intel_pmu_disable_all
     3.92%  sched-pipe  [kernel.vmlinux]    [k] switch_mm_irqs_off
     3.71%  sched-pipe  perf                [.] worker_thread

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: 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: Ingo Molnar <mingo@kernel.org>
include/linux/perf_event.h
kernel/events/core.c