From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753549AbaHEORf (ORCPT ); Tue, 5 Aug 2014 10:17:35 -0400 Received: from mga01.intel.com ([192.55.52.88]:19439 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752041AbaHEORe (ORCPT ); Tue, 5 Aug 2014 10:17:34 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.01,804,1400050800"; d="scan'208";a="580303037" Date: Tue, 5 Aug 2014 07:17:33 -0700 From: Andi Kleen To: Ingo Molnar Cc: Arnaldo Carvalho de Melo , linux-kernel@vger.kernel.org, Andi Kleen , Peter Zijlstra , Stephane Eranian , Arnaldo Carvalho de Melo , Thomas Gleixner , Jiri Olsa Subject: Re: [PATCH 05/33] perf record: Allow the user to disable time stamps Message-ID: <20140805141733.GH5803@tassilo.jf.intel.com> References: <1407169064-25625-1-git-send-email-acme@kernel.org> <1407169064-25625-6-git-send-email-acme@kernel.org> <20140805060856.GA9453@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140805060856.GA9453@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > Time stamps are always implicitely enabled for record currently. The > > old --time/-T option is a nop. > > > > Allow the user to disable timestamps by using --no-time > > > > This can cause some minor misaccounting (by missing mmaps), but > > significantly lowers the size of perf.data > > I'm not any big change in size: > > -rw------- 1 mingo mingo 384768 Aug 5 08:01 perf.data.timestamps > -rw------- 1 mingo mingo 336952 Aug 5 08:00 perf.data.notimestamps It will depend on your workload. What period did you use (or did it automatically use) and what kind of workload was it? The smaller the period, the higher the benefit. There are some classes of workloads where using a smaller period is especially beneficial, essentially anything with lots of small events, instead of long loops. You also get a higher benefit if you use -c or -F, because without that each sample is smaller (no period reported) You also get higher benefit for longer traces, and traces that do not start a lot of programs, as those tend to be dominated by MMAP events and other overhead. > So either remove the --time option altogether, or fix its > 'misaccounting' so that the profile can be relied on. I don't know how to fix it. Do you? I guess one possible way to mitigate would be to lower the perf buffer sizes, then the worst case out of ordering would be less (I believe any potential problem just comes from out of order events). However that may impact performance. -Andi