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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 22EB3C43331 for ; Tue, 31 Mar 2020 16:10:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EC347206CC for ; Tue, 31 Mar 2020 16:10:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gJRVfj1W" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731053AbgCaQKS (ORCPT ); Tue, 31 Mar 2020 12:10:18 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:60236 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730562AbgCaQKS (ORCPT ); Tue, 31 Mar 2020 12:10:18 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585671017; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Voe2qrXDe5Yx0QpIR9//IUXba58ao3Ab+K8YcD8EZhE=; b=gJRVfj1WzoxhrSnEx+8KlaXm9HdEf5Q74ZbxbAqXlKcCSptOxCDnG+QH1ItbfDe+oO23Zj fUCzR6Jw7cv/NQSgStyw94/t9RJLv5Sh3C5k+KItlK+ohz04CV8ypv6tEppnyj8JhJtc5r zNG+9KrtxMOd/jMo4GVUcludHSeWPdI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-343-l_hc7TnpMfu61olT8aiA3A-1; Tue, 31 Mar 2020 12:10:12 -0400 X-MC-Unique: l_hc7TnpMfu61olT8aiA3A-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8B6CF13FB; Tue, 31 Mar 2020 16:10:08 +0000 (UTC) Received: from sandy.ghostprotocols.net (unknown [10.3.128.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 69BB05E009; Tue, 31 Mar 2020 16:10:07 +0000 (UTC) Received: by sandy.ghostprotocols.net (Postfix, from userid 1000) id 92C9182; Tue, 31 Mar 2020 13:10:02 -0300 (BRT) Date: Tue, 31 Mar 2020 13:10:02 -0300 From: Arnaldo Carvalho de Melo To: Milian Wolff Cc: ahmadkhorrami , 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 Message-ID: <20200331161002.GB23207@redhat.com> References: <821540886fc57d7749edee585a50602f@ut.ac.ir> <8573002.CDJkKcVGEf@agathebauer> <7774721.NyiUUSuA9g@agathebauer> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <7774721.NyiUUSuA9g@agathebauer> X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.5.20 (2009-12-10) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Content-Transfer-Encoding: quoted-printable Sender: linux-trace-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-trace-users@vger.kernel.org Em Tue, Mar 31, 2020 at 05:29:17PM +0200, Milian Wolff escreveu: > On Dienstag, 31. M=E4rz 2020 17:02:37 CEST ahmadkhorrami wrote: > > Hi Milian, > > Thanks for the detailed answer. Well, the bug you mentioned is bad ne= ws. > > Because I sample using uppp. Perhaps this leads to these weird traces= . >=20 > Please read the full thread from here on: >=20 > https://lkml.org/lkml/2018/11/2/86 >=20 > But as I said - it should be easy to check if this is really the issue = are=20 > running into or not: Try to see if you see the problem when you sample = without=20 > `ppp`. If not, then you can be pretty sure it's this issue. If you stil= l see=20 > it, then it's something different. >=20 > > Is this a purely software bug? >=20 > I wouldn't call it that, personally. Rather, it's a limitation in the h= ardware=20 > and software. We would need something completely different to "fix" thi= s, i.e.=20 > something like a deeper LBR. That's btw another alternative you could t= ry:=20 > `perf record --call-graph lbr` and live with the short call stacks. But= at=20 > least these should be correct (afaik). For me personally they are alway= s far=20 > 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.int= el.com/ - Arnaldo