Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934401AbZKYJ6a (ORCPT ); Wed, 25 Nov 2009 04:58:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758400AbZKYJ6a (ORCPT ); Wed, 25 Nov 2009 04:58:30 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:56781 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753754AbZKYJ63 (ORCPT ); Wed, 25 Nov 2009 04:58:29 -0500 Subject: Re: [RFC][PATCH 0/7] perf trace: general-purpose scripting support, v2 From: Peter Zijlstra To: Ingo Molnar Cc: Tom Zanussi , linux-kernel@vger.kernel.org, fweisbec@gmail.com, rostedt@goodmis.org, anton@samba.org, hch@infradead.org, Mike Galbraith In-Reply-To: <20091125094338.GA21220@elte.hu> References: <1259133352-23685-1-git-send-email-tzanussi@gmail.com> <1259137695.4027.45.camel@laptop> <1259141891.4027.199.camel@laptop> <20091125094338.GA21220@elte.hu> Content-Type: text/plain; charset="UTF-8" Date: Wed, 25 Nov 2009 10:58:29 +0100 Message-ID: <1259143109.4027.241.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1861 Lines: 38 On Wed, 2009-11-25 at 10:43 +0100, Ingo Molnar wrote: > * Peter Zijlstra wrote: > > > On Wed, 2009-11-25 at 09:28 +0100, Peter Zijlstra wrote: > > > On Wed, 2009-11-25 at 01:15 -0600, Tom Zanussi wrote: > > > > sched::sched_wakeup 0 01238.657997033 6183 firefox comm=firefox, pid=6199, prio=120, success=1, target_cpu=1 > > > > sched::sched_switch 1 01238.657991740 7140 firefox prev_comm=firefox, prev_pid=7140, prev_prio=120, prev_state=S, next_comm=firefox, next_pid=6199, next_prio=120 > > > > > > > > min_wakeup_latency: -5293 > > > > > > Looks like we missed a clock update on the cross cpu wakeup, Mike was > > > busy plugging those holes -- I've been starting at a patch that might > > > cure this (amongst other things). > > > > Hmm, current -tip should have that cured as per: > > well, but timestamp inconsistencies are still possible fundamentally, as > cpu_clock() is not globally serialized. No, but the cross-cpu update should have pulled 1 to the same time as 0. So what we see here is that at wakeup time, cpu0 has 01238.657997033, if it at that time does a cross-cpu clock update, sched_clock_remote() should pull cpu1's time to that same time (unless cpu1 is ahead, but given the situation that's clearly not the case). The clock update on cpu1's schedule() would then either find a negative increment, not further updating the time, but refreshing the raw tsc stamp so that future updates appear monotonic, or find a positive stamp, resulting in fwd time movement. In any case, the wakeup latency should appear >= 0. -- 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/