From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnaldo Carvalho de Melo Subject: Re: Size of perf data files Date: Thu, 27 Nov 2014 10:19:16 -0300 Message-ID: <20141127131916.GH30226@kernel.org> References: <1601237.BEhNSa8l6d@milian-kdab2> <20141126160617.GD30226@kernel.org> <1439400.fEBkspRaxp@milian-kdab2> <87oarto40a.fsf@sejong.aot.lge.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail.kernel.org ([198.145.19.201]:32802 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750784AbaK0NTX (ORCPT ); Thu, 27 Nov 2014 08:19:23 -0500 Content-Disposition: inline In-Reply-To: <87oarto40a.fsf@sejong.aot.lge.com> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Namhyung Kim Cc: Milian Wolff , linux-perf-users Em Thu, Nov 27, 2014 at 09:56:21AM +0900, Namhyung Kim escreveu: > Hi Milian, > > On Wed, 26 Nov 2014 19:11:01 +0100, Milian Wolff wrote: > > I tried this on a benchmark of mine: > > > > before: > > [ perf record: Woken up 196 times to write data ] > > [ perf record: Captured and wrote 48.860 MB perf.data (~2134707 samples) ] > > > > after, with dwarf,512 > > [ perf record: Woken up 18 times to write data ] > > [ perf record: Captured and wrote 4.401 MB perf.data (~192268 samples) ] > > > > What confuses me though is the number of samples. When the workload is equal, > > shouldn't the number of samples stay the same? Or what does this mean? The > > resulting reports both look similar enough. > > It's bogus - it just calculates the number of samples based on the file > size (with fixed sample size). I think we should either show the correct > number as we post-process samples for build-id detection or simply > remove it. Well, since we setup the perf_event_attr we could perhaps do a better job at estimating this... In this case we even know how much stack_dump we will take at each sample, that would be major culprit for the current mis estimation. And yes, if we do the post processing, we can do a precise calculation. - Arnaldo