From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757551Ab0JRTSY (ORCPT ); Mon, 18 Oct 2010 15:18:24 -0400 Received: from hera.kernel.org ([140.211.167.34]:59360 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757470Ab0JRTSX (ORCPT ); Mon, 18 Oct 2010 15:18:23 -0400 Date: Mon, 18 Oct 2010 19:17:58 GMT From: tip-bot for Stephane Eranian Cc: linux-kernel@vger.kernel.org, eranian@google.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, eranian@google.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, tglx@linutronix.de, mingo@elte.hu In-Reply-To: <4cb856dc.51edd80a.5ae0.38fb@mx.google.com> References: <4cb856dc.51edd80a.5ae0.38fb@mx.google.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/core] perf_events: Fix bogus context time tracking Message-ID: Git-Commit-ID: c530ccd9a1864a44a7ff35826681229ce9f2357a X-Mailer: tip-git-log-daemon MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.3 (hera.kernel.org [127.0.0.1]); Mon, 18 Oct 2010 19:17:59 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: c530ccd9a1864a44a7ff35826681229ce9f2357a Gitweb: http://git.kernel.org/tip/c530ccd9a1864a44a7ff35826681229ce9f2357a Author: Stephane Eranian AuthorDate: Fri, 15 Oct 2010 15:26:01 +0200 Committer: Ingo Molnar CommitDate: Mon, 18 Oct 2010 19:58:46 +0200 perf_events: Fix bogus context time tracking You can only call update_context_time() when the context is active, i.e., the thread it is attached to is still running. However, perf_event_read() can be called even when the context is inactive, e.g., user read() the counters. The call to update_context_time() must be conditioned on the status of the context, otherwise, bogus time_enabled, time_running may be returned. Here is an example on AMD64. The task program is an example from libpfm4. The -p prints deltas every 1s. $ task -p -e cpu_clk_unhalted sleep 5 2,266,610 cpu_clk_unhalted (0.00% scaling, ena=2,158,982, run=2,158,982) 0 cpu_clk_unhalted (0.00% scaling, ena=2,158,982, run=2,158,982) 0 cpu_clk_unhalted (0.00% scaling, ena=2,158,982, run=2,158,982) 0 cpu_clk_unhalted (0.00% scaling, ena=2,158,982, run=2,158,982) 0 cpu_clk_unhalted (0.00% scaling, ena=2,158,982, run=2,158,982) 5,242,358,071 cpu_clk_unhalted (99.95% scaling, ena=5,000,359,984, run=2,319,270) Whereas if you don't read deltas, e.g., no call to perf_event_read() until the process terminates: $ task -e cpu_clk_unhalted sleep 5 2,497,783 cpu_clk_unhalted (0.00% scaling, ena=2,376,899, run=2,376,899) Notice that time_enable, time_running are bogus in the first example causing bogus scaling. This patch fixes the problem, by conditionally calling update_context_time() in perf_event_read(). Signed-off-by: Stephane Eranian Signed-off-by: Peter Zijlstra Cc: stable@kernel.org LKML-Reference: <4cb856dc.51edd80a.5ae0.38fb@mx.google.com> Signed-off-by: Ingo Molnar --- kernel/perf_event.c | 8 +++++++- 1 files changed, 7 insertions(+), 1 deletions(-) diff --git a/kernel/perf_event.c b/kernel/perf_event.c index 1ec3916..e7eeba1 100644 --- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -1780,7 +1780,13 @@ static u64 perf_event_read(struct perf_event *event) unsigned long flags; raw_spin_lock_irqsave(&ctx->lock, flags); - update_context_time(ctx); + /* + * may read while context is not active + * (e.g., thread is blocked), in that case + * we cannot update context time + */ + if (ctx->is_active) + update_context_time(ctx); update_event_times(event); raw_spin_unlock_irqrestore(&ctx->lock, flags); }