diff options
author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2011-11-16 14:38:16 +0100 |
---|---|---|
committer | Ingo Molnar <mingo@elte.hu> | 2011-12-06 08:33:52 +0100 |
commit | 0f5a2601284237e2ba089389fd75d67f77626cef (patch) | |
tree | 37eedc660f09a36cfbd6b2a2c28e8cd0d1dbe167 /kernel/events | |
parent | d6c1c49de577fa292af2449817364b7d89b574d8 (diff) | |
download | linux-0f5a2601284237e2ba089389fd75d67f77626cef.tar.bz2 |
perf: Avoid a useless pmu_disable() in the perf-tick
Gleb writes:
> Currently pmu is disabled and re-enabled on each timer interrupt even
> when no rotation or frequency adjustment is needed. On Intel CPU this
> results in two writes into PERF_GLOBAL_CTRL MSR per tick. On bare metal
> it does not cause significant slowdown, but when running perf in a virtual
> machine it leads to 20% slowdown on my machine.
Cure this by keeping a perf_event_context::nr_freq counter that counts the
number of active events that require frequency adjustments and use this in a
similar fashion to the already existing nr_events != nr_active test in
perf_rotate_context().
By being able to exclude both rotation and frequency adjustments a-priory for
the common case we can avoid the otherwise superfluous PMU disable.
Suggested-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-515yhoatehd3gza7we9fapaa@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/events')
-rw-r--r-- | kernel/events/core.c | 48 |
1 files changed, 32 insertions, 16 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index a355ffb0b28f..b3fed52aaf20 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1130,6 +1130,8 @@ event_sched_out(struct perf_event *event, if (!is_software_event(event)) cpuctx->active_oncpu--; ctx->nr_active--; + if (event->attr.freq && event->attr.sample_freq) + ctx->nr_freq--; if (event->attr.exclusive || !cpuctx->active_oncpu) cpuctx->exclusive = 0; } @@ -1407,6 +1409,8 @@ event_sched_in(struct perf_event *event, if (!is_software_event(event)) cpuctx->active_oncpu++; ctx->nr_active++; + if (event->attr.freq && event->attr.sample_freq) + ctx->nr_freq++; if (event->attr.exclusive) cpuctx->exclusive = 1; @@ -2329,6 +2333,9 @@ static void perf_ctx_adjust_freq(struct perf_event_context *ctx, u64 period) u64 interrupts, now; s64 delta; + if (!ctx->nr_freq) + return; + list_for_each_entry_rcu(event, &ctx->event_list, event_entry) { if (event->state != PERF_EVENT_STATE_ACTIVE) continue; @@ -2384,12 +2391,14 @@ static void perf_rotate_context(struct perf_cpu_context *cpuctx) { u64 interval = (u64)cpuctx->jiffies_interval * TICK_NSEC; struct perf_event_context *ctx = NULL; - int rotate = 0, remove = 1; + int rotate = 0, remove = 1, freq = 0; if (cpuctx->ctx.nr_events) { remove = 0; if (cpuctx->ctx.nr_events != cpuctx->ctx.nr_active) rotate = 1; + if (cpuctx->ctx.nr_freq) + freq = 1; } ctx = cpuctx->task_ctx; @@ -2397,33 +2406,40 @@ static void perf_rotate_context(struct perf_cpu_context *cpuctx) remove = 0; if (ctx->nr_events != ctx->nr_active) rotate = 1; + if (ctx->nr_freq) + freq = 1; } + if (!rotate && !freq) + goto done; + perf_ctx_lock(cpuctx, cpuctx->task_ctx); perf_pmu_disable(cpuctx->ctx.pmu); - perf_ctx_adjust_freq(&cpuctx->ctx, interval); - if (ctx) - perf_ctx_adjust_freq(ctx, interval); - if (!rotate) - goto done; + if (freq) { + perf_ctx_adjust_freq(&cpuctx->ctx, interval); + if (ctx) + perf_ctx_adjust_freq(ctx, interval); + } - cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE); - if (ctx) - ctx_sched_out(ctx, cpuctx, EVENT_FLEXIBLE); + if (rotate) { + cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE); + if (ctx) + ctx_sched_out(ctx, cpuctx, EVENT_FLEXIBLE); - rotate_ctx(&cpuctx->ctx); - if (ctx) - rotate_ctx(ctx); + rotate_ctx(&cpuctx->ctx); + if (ctx) + rotate_ctx(ctx); + + perf_event_sched_in(cpuctx, ctx, current); + } - perf_event_sched_in(cpuctx, ctx, current); + perf_pmu_enable(cpuctx->ctx.pmu); + perf_ctx_unlock(cpuctx, cpuctx->task_ctx); done: if (remove) list_del_init(&cpuctx->rotation_list); - - perf_pmu_enable(cpuctx->ctx.pmu); - perf_ctx_unlock(cpuctx, cpuctx->task_ctx); } void perf_event_task_tick(void) |