From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DD771C43331 for ; Tue, 31 Mar 2020 20:57:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B23AC2080C for ; Tue, 31 Mar 2020 20:57:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727852AbgCaU5s (ORCPT ); Tue, 31 Mar 2020 16:57:48 -0400 Received: from mail.ut.ac.ir ([80.66.177.10]:56778 "EHLO mail.ut.ac.ir" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728893AbgCaU5s (ORCPT ); Tue, 31 Mar 2020 16:57:48 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.ut.ac.ir (Postfix) with ESMTP id 2669CF80AA; Wed, 1 Apr 2020 01:27:45 +0430 (+0430) Received: from mail.ut.ac.ir ([127.0.0.1]) by localhost (mail.ut.ac.ir [127.0.0.1]) (amavisd-new, port 10024) with LMTP id 1l8-GxAazV2K; Wed, 1 Apr 2020 01:27:44 +0430 (+0430) Received: from mail.ut.ac.ir (mail.ut.ac.ir [194.225.0.10]) by mail.ut.ac.ir (Postfix) with ESMTP id E4031F80A9; Wed, 1 Apr 2020 01:27:43 +0430 (+0430) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Wed, 01 Apr 2020 01:27:43 +0430 From: ahmadkhorrami To: Milian Wolff Cc: Jiri Olsa , Steven Rostedt , Arnaldo Carvalho de Melo , Linux-trace Users , Peter Zijlstra , linux-trace-users-owner@vger.kernel.org, Jin Yao , Namhyung Kim , Andi Kleen Subject: Re: Wrong Perf Backtraces In-Reply-To: <7774721.NyiUUSuA9g@agathebauer> References: <821540886fc57d7749edee585a50602f@ut.ac.ir> <8573002.CDJkKcVGEf@agathebauer> <7774721.NyiUUSuA9g@agathebauer> Message-ID: X-Sender: ahmadkhorrami@ut.ac.ir User-Agent: Roundcube Webmail/1.3.6 Sender: linux-trace-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-trace-users@vger.kernel.org Hi, On 2020-03-31 19:59, Milian Wolff wrote: > On Dienstag, 31. März 2020 17:02:37 CEST ahmadkhorrami wrote: > >> Hi Milian, >> Thanks for the detailed answer. Well, the bug you mentioned is bad >> news. >> Because I sample using uppp. Perhaps this leads to these weird traces. > > Please read the full thread from here on: > > https://lkml.org/lkml/2018/11/2/86 > > But as I said - it should be easy to check if this is really the issue > are > running into or not: Try to see if you see the problem when you sample > without > `ppp`. If not, then you can be pretty sure it's this issue. If you > still see > it, then it's something different. > Well, the problem exists even when ":uppp" is changed to ":u". >> Is this a purely software bug? > > I wouldn't call it that, personally. Rather, it's a limitation in the > hardware > and software. We would need something completely different to "fix" > this, i.e. > something like a deeper LBR. That's btw another alternative you could > try: > `perf record --call-graph lbr` and live with the short call stacks. But > at > least these should be correct (afaik). For me personally they are > always far > too short and thus not practical to use in reality. > > Cheers Regards.