From mboxrd@z Thu Jan 1 00:00:00 1970 From: Milian Wolff Subject: Re: Wildly different output sizes between subsequent perf record runs. Date: Mon, 06 Nov 2017 13:06:56 +0100 Message-ID: <5922369.x0IdO5xPIl@agathebauer> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: Received: from mail.kdab.com ([176.9.126.58]:39284 "EHLO mail.kdab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752617AbdKFMHA (ORCPT ); Mon, 6 Nov 2017 07:07:00 -0500 In-Reply-To: Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Bram Stolk Cc: linux-perf-users@vger.kernel.org, Arnaldo Carvalho 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