Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754554AbZI3VBt (ORCPT ); Wed, 30 Sep 2009 17:01:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754397AbZI3VBt (ORCPT ); Wed, 30 Sep 2009 17:01:49 -0400 Received: from hera.kernel.org ([140.211.167.34]:43959 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754156AbZI3VBq (ORCPT ); Wed, 30 Sep 2009 17:01:46 -0400 Date: Wed, 30 Sep 2009 21:01:13 GMT From: tip-bot for Eric Dumazet Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@redhat.com, eric.dumazet@gmail.com, a.p.zijlstra@chello.nl, johnstul@us.ibm.com, torvalds@linux-foundation.org, arjan@linux.intel.com, schwidefsky@de.ibm.com, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, eric.dumazet@gmail.com, arjan@linux.intel.com, torvalds@linux-foundation.org, johnstul@us.ibm.com, a.p.zijlstra@chello.nl, schwidefsky@de.ibm.com, tglx@linutronix.de, mingo@elte.hu In-Reply-To: <20090930170754.0886ff2e@infradead.org> References: <20090930170754.0886ff2e@infradead.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/urgent] sched_clock: Fix atomicity/continuity bug by using cmpxchg64() Message-ID: Git-Commit-ID: 152f9d0710a62708710161bce1b29fa8292c8c11 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-4.0 (hera.kernel.org [127.0.0.1]); Wed, 30 Sep 2009 21:01:14 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2214 Lines: 65 Commit-ID: 152f9d0710a62708710161bce1b29fa8292c8c11 Gitweb: http://git.kernel.org/tip/152f9d0710a62708710161bce1b29fa8292c8c11 Author: Eric Dumazet AuthorDate: Wed, 30 Sep 2009 20:36:19 +0200 Committer: Ingo Molnar CommitDate: Wed, 30 Sep 2009 22:56:10 +0200 sched_clock: Fix atomicity/continuity bug by using cmpxchg64() Commit def0a9b2573 (sched_clock: Make it NMI safe) assumed cmpxchg() of 64bit values was available on X86_32. That is not so - and causes some subtle scheduler misbehavior due to incorrect timestamps off to up by ~4 seconds. Two symptoms are known right now: - interactivity problems seen by Arjan: up to 600 msecs latencies instead of the expected 20-40 msecs. These latencies are very visible on the desktop. - incorrect CPU stats: occasionally too high percentages in 'top', and crazy CPU usage stats. Reported-by: Martin Schwidefsky Signed-off-by: Eric Dumazet Signed-off-by: Arjan van de Ven Acked-by: Linus Torvalds Cc: John Stultz Cc: Peter Zijlstra LKML-Reference: <20090930170754.0886ff2e@infradead.org> Signed-off-by: Ingo Molnar --- kernel/sched_clock.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c index ac2e1dc..479ce56 100644 --- a/kernel/sched_clock.c +++ b/kernel/sched_clock.c @@ -127,7 +127,7 @@ again: clock = wrap_max(clock, min_clock); clock = wrap_min(clock, max_clock); - if (cmpxchg(&scd->clock, old_clock, clock) != old_clock) + if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock) goto again; return clock; @@ -163,7 +163,7 @@ again: val = remote_clock; } - if (cmpxchg(ptr, old_val, val) != old_val) + if (cmpxchg64(ptr, old_val, val) != old_val) goto again; return val; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/