From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 65948C43219 for ; Mon, 29 Apr 2019 15:04:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3735C20651 for ; Mon, 29 Apr 2019 15:04:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728595AbfD2PEt (ORCPT ); Mon, 29 Apr 2019 11:04:49 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:59820 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728253AbfD2PEs (ORCPT ); Mon, 29 Apr 2019 11:04:48 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D99E680D; Mon, 29 Apr 2019 08:04:47 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 503A83F5C1; Mon, 29 Apr 2019 08:04:46 -0700 (PDT) Date: Mon, 29 Apr 2019 16:04:43 +0100 From: Mark Rutland To: kan.liang@linux.intel.com Cc: peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, linux-kernel@vger.kernel.org, eranian@google.com, tj@kernel.org, ak@linux.intel.com Subject: Re: [PATCH 1/4] perf: Fix system-wide events miscounting during cgroup monitoring Message-ID: <20190429150443.GB2182@lakrids.cambridge.arm.com> References: <1556549045-71814-1-git-send-email-kan.liang@linux.intel.com> <1556549045-71814-2-git-send-email-kan.liang@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1556549045-71814-2-git-send-email-kan.liang@linux.intel.com> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 29, 2019 at 07:44:02AM -0700, kan.liang@linux.intel.com wrote: > From: Kan Liang > > When counting system-wide events and cgroup events simultaneously, the > value of system-wide events are miscounting. For example, > > perf stat -e cycles,instructions -e cycles,instructions -G > cgroup1,cgroup1,cgroup2,cgroup2 -a -e cycles,instructions -I 1000 > > 1.096265502 12,375,398,872 cycles cgroup1 > 1.096265502 8,396,184,503 instructions cgroup1 > # 0.10 insn per cycle > 1.096265502 109,609,027,112 cycles cgroup2 > 1.096265502 11,533,690,148 instructions cgroup2 > # 0.14 insn per cycle > 1.096265502 121,672,937,058 cycles > 1.096265502 19,331,496,727 instructions # > 0.24 insn per cycle > > The events are identical events for system-wide and cgroup. The > value of system-wide events is less than the sum of cgroup events, > which is wrong. > > Both system-wide and cgroup are per-cpu. They share the same cpuctx > groups, cpuctx->flexible_groups/pinned_groups. > In context switch, cgroup switch tries to schedule all the events in > the cpuctx groups. The unmatched cgroup events can be filtered by its > event->cgrp. However, system-wide events, which event->cgrp is NULL, are > unconditionally switched, which causes miscounting. Why exactly does that cause mis-counting? Are the system-wide events not switched back in? Or filtered erroneously? > Introduce cgrp_switch in cpuctx to indicate the cgroup context switch. > If it's system-wide event in context switch, don't try to switch it. > > Fixes: e5d1367f17ba ("perf: Add cgroup support") > Signed-off-by: Kan Liang > --- > include/linux/perf_event.h | 1 + > kernel/events/core.c | 30 ++++++++++++++++++++++++++++-- > 2 files changed, 29 insertions(+), 2 deletions(-) > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index e47ef76..039e2f2 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -795,6 +795,7 @@ struct perf_cpu_context { > #ifdef CONFIG_CGROUP_PERF > struct perf_cgroup *cgrp; > struct list_head cgrp_cpuctx_entry; > + unsigned int cgrp_switch :1; > #endif > > struct list_head sched_cb_entry; > diff --git a/kernel/events/core.c b/kernel/events/core.c > index dc7dead..388dd42 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -809,6 +809,7 @@ static void perf_cgroup_switch(struct task_struct *task, int mode) > > perf_ctx_lock(cpuctx, cpuctx->task_ctx); > perf_pmu_disable(cpuctx->ctx.pmu); > + cpuctx->cgrp_switch = true; > > if (mode & PERF_CGROUP_SWOUT) { > cpu_ctx_sched_out(cpuctx, EVENT_ALL); > @@ -832,6 +833,7 @@ static void perf_cgroup_switch(struct task_struct *task, int mode) > &cpuctx->ctx); > cpu_ctx_sched_in(cpuctx, EVENT_ALL, task); > } > + cpuctx->cgrp_switch = false; > perf_pmu_enable(cpuctx->ctx.pmu); > perf_ctx_unlock(cpuctx, cpuctx->task_ctx); > } > @@ -2944,13 +2946,25 @@ static void ctx_sched_out(struct perf_event_context *ctx, > > perf_pmu_disable(ctx->pmu); > if (is_active & EVENT_PINNED) { > - list_for_each_entry_safe(event, tmp, &ctx->pinned_active, active_list) > + list_for_each_entry_safe(event, tmp, &ctx->pinned_active, active_list) { > +#ifdef CONFIG_CGROUP_PERF > + /* Don't sched system-wide event when cgroup context switch */ > + if (cpuctx->cgrp_switch && !event->cgrp) > + continue; > +#endif This pattern is duplicated several times, and should probably be a helper like: static bool skip_cgroup_switch(struct perf_cpu_context *cpuctx, struct perf_event *event); { return IS_ENABLED(CONFIG_CGROUP_PERF) && cpuctx->cgrp_switch && !event->cgrp; } ... allowing the above to be an unconditional: if (skip_cgroup_switch(cpuctx, event)) continue; ... and likewise for the other cases. Thanks, Mark. > group_sched_out(event, cpuctx, ctx); > + } > } > > if (is_active & EVENT_FLEXIBLE) { > - list_for_each_entry_safe(event, tmp, &ctx->flexible_active, active_list) > + list_for_each_entry_safe(event, tmp, &ctx->flexible_active, active_list) { > +#ifdef CONFIG_CGROUP_PERF > + /* Don't sched system-wide event when cgroup context switch */ > + if (cpuctx->cgrp_switch && !event->cgrp) > + continue; > +#endif > group_sched_out(event, cpuctx, ctx); > + } > } > perf_pmu_enable(ctx->pmu); > } > @@ -3280,6 +3294,12 @@ static int pinned_sched_in(struct perf_event *event, void *data) > if (event->state <= PERF_EVENT_STATE_OFF) > return 0; > > +#ifdef CONFIG_CGROUP_PERF > + /* Don't sched system-wide event when cgroup context switch */ > + if (sid->cpuctx->cgrp_switch && !event->cgrp) > + return 0; > +#endif > + > if (!event_filter_match(event)) > return 0; > > @@ -3305,6 +3325,12 @@ static int flexible_sched_in(struct perf_event *event, void *data) > if (event->state <= PERF_EVENT_STATE_OFF) > return 0; > > +#ifdef CONFIG_CGROUP_PERF > + /* Don't sched system-wide event when cgroup context switch */ > + if (sid->cpuctx->cgrp_switch && !event->cgrp) > + return 0; > +#endif > + > if (!event_filter_match(event)) > return 0; > > -- > 2.7.4 >