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 21779C43331 for ; Tue, 31 Mar 2020 19:20:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EF1D820784 for ; Tue, 31 Mar 2020 19:20:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727720AbgCaTUy (ORCPT ); Tue, 31 Mar 2020 15:20:54 -0400 Received: from mail.ut.ac.ir ([80.66.177.10]:37462 "EHLO mail.ut.ac.ir" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727509AbgCaTUy (ORCPT ); Tue, 31 Mar 2020 15:20:54 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.ut.ac.ir (Postfix) with ESMTP id 69F721DB1BB; Tue, 31 Mar 2020 23:50:51 +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 y6-LkbiTIigQ; Tue, 31 Mar 2020 23:50:50 +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 E5F741DB172; Tue, 31 Mar 2020 23:50:49 +0430 (+0430) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Tue, 31 Mar 2020 23:50:49 +0430 From: ahmadkhorrami To: Arnaldo Carvalho de Melo Cc: Milian Wolff , Jiri Olsa , Steven Rostedt , 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: <20200331161002.GB23207@redhat.com> References: <821540886fc57d7749edee585a50602f@ut.ac.ir> <8573002.CDJkKcVGEf@agathebauer> <7774721.NyiUUSuA9g@agathebauer> <20200331161002.GB23207@redhat.com> Message-ID: <56139d1ce9afdfe5fdea0a0a374c5faf@ut.ac.ir> 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 Archived-At: List-Archive: List-Post: Thanks. I checked "perf script -D", and it contains repeated addresses in itself. The problem seems to occur at the sampling instant. Does anybody know the location of the sampling handler? I am looking forward to the answer. Regards. On 2020-03-31 20:40, Arnaldo Carvalho de Melo wrote: > Em Tue, Mar 31, 2020 at 05:29:17PM +0200, Milian Wolff escreveu: 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. > > 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. Probably this may help: From: Kan Liang Subject: [PATCH V4 00/17] Stitch LBR call stack (Perf Tools) Date: Thu, 19 Mar 2020 13:25:00 -0700 https://lore.kernel.org/lkml/20200319202517.23423-1-kan.liang@linux.intel.com/ - Arnaldo