From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933090Ab1LFJoA (ORCPT ); Tue, 6 Dec 2011 04:44:00 -0500 Received: from terminus.zytor.com ([198.137.202.10]:34793 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932959Ab1LFJn6 (ORCPT ); Tue, 6 Dec 2011 04:43:58 -0500 Date: Tue, 6 Dec 2011 01:43:32 -0800 From: tip-bot for Peter Zijlstra Message-ID: Cc: linux-kernel@vger.kernel.org, gleb@redhat.com, hpa@zytor.com, mingo@redhat.com, a.p.zijlstra@chello.nl, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, gleb@redhat.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, tglx@linutronix.de, mingo@elte.hu To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/core] perf: Avoid a useless pmu_disable() in the perf-tick Git-Commit-ID: 0f5a2601284237e2ba089389fd75d67f77626cef X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.6 (terminus.zytor.com [127.0.0.1]); Tue, 06 Dec 2011 01:43:37 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 0f5a2601284237e2ba089389fd75d67f77626cef Gitweb: http://git.kernel.org/tip/0f5a2601284237e2ba089389fd75d67f77626cef Author: Peter Zijlstra AuthorDate: Wed, 16 Nov 2011 14:38:16 +0100 Committer: Ingo Molnar CommitDate: Tue, 6 Dec 2011 08:33:52 +0100 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 Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/n/tip-515yhoatehd3gza7we9fapaa@git.kernel.org Signed-off-by: Ingo Molnar --- include/linux/perf_event.h | 1 + kernel/events/core.c | 48 +++++++++++++++++++++++++++++-------------- 2 files changed, 33 insertions(+), 16 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index b1f8912..cb44c9e 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -890,6 +890,7 @@ struct perf_event_context { int nr_active; int is_active; int nr_stat; + int nr_freq; int rotate_disable; atomic_t refcount; struct task_struct *task; diff --git a/kernel/events/core.c b/kernel/events/core.c index a355ffb..b3fed52 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)