From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bram Stolk Subject: Re: Wildly different output sizes between subsequent perf record runs. Date: Mon, 6 Nov 2017 09:38:18 -0800 Message-ID: References: <5922369.x0IdO5xPIl@agathebauer> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: Received: from mail-vk0-f47.google.com ([209.85.213.47]:51918 "EHLO mail-vk0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751890AbdKFRiT (ORCPT ); Mon, 6 Nov 2017 12:38:19 -0500 Received: by mail-vk0-f47.google.com with SMTP id v3so6250610vkb.8 for ; Mon, 06 Nov 2017 09:38:19 -0800 (PST) In-Reply-To: <5922369.x0IdO5xPIl@agathebauer> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Milian Wolff Cc: linux-perf-users@vger.kernel.org, Arnaldo Carvalho Thanks Milian, This issue is too elusive. Today I can no longer reproduce the issue with short data runs, even though I use the same perf binary on the same system with same arguments. Not sure what has changed. I'll try to reboot and try again, see if I can trigger it on a 'colder' machine. On Mon, Nov 6, 2017 at 4:06 AM, Milian Wolff wrote: > On Samstag, 4. November 2017 02:57:01 CET Bram Stolk wrote: >> If I do subsequent runs of 'perf record', both of which are identical, >> I sometimes get wildly different output sizes. >> >> >> https://gist.github.com/stolk/3666b2b4d4319764fdff4a2d4c619782 >> >> The binary did the same amount of work, and took the same amount of >> time to execute. >> This is with using perf from Ubuntu LTS. > > I think this is the same bug that I have raised before. See https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1479712.html and below. > > Can you try to run your command with a constant period (`-c 3000000` or > similar), instead of using a dynamic period (i.e. `--freq`)? Does the issue go > away then? If yes, then it's the same issue that I described earlier, which > noone else from the perf team has acknowledged so far. I know multiple people > who are affected by this though... > > -- > Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer > KDAB (Deutschland) GmbH&Co KG, a KDAB Group company > Tel: +49-30-521325470 > KDAB - The Qt Experts > > -- Owner/Director of Game Studio Abraham Stolk Inc. Vancouver BC, Canada b.stolk@gmail.com