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=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 77319C43331 for ; Tue, 31 Mar 2020 15:29:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 439B420786 for ; Tue, 31 Mar 2020 15:29:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kdab.com header.i=@kdab.com header.b="MCEdT+81" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730541AbgCaP3Y (ORCPT ); Tue, 31 Mar 2020 11:29:24 -0400 Received: from mail.kdab.com ([176.9.126.58]:23067 "EHLO mail.kdab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730391AbgCaP3X (ORCPT ); Tue, 31 Mar 2020 11:29:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kdab.com; h= content-type:content-type:mime-version:references:in-reply-to :organization:message-id:date:date:subject:subject:from:from; s= dkim; t=1585668558; x=1586532559; bh=QKN4nB+vUQCq7cCZ74ZJU3mR2xq ZlWfHXc3Y8t1Ly7c=; b=MCEdT+81qgbRxxqC4QLHP2o8I0IQQc5w3/TZ9714exh CXf6oi+6NdXpHpxeLohP5Jvq5nAMcMbVOT36YhzH3dTAPgu40OYML2GS1XkVHdJA xzvjn6u3blGb3xFYU7L5BuQFwTw8kKCTeoIL3BPgXwX3u6AYfZG3ciI+vZjjr1pc = X-Virus-Scanned: amavisd-new at kdab.com From: Milian Wolff To: ahmadkhorrami 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 Date: Tue, 31 Mar 2020 17:29:17 +0200 Message-ID: <7774721.NyiUUSuA9g@agathebauer> Organization: KDAB In-Reply-To: References: <821540886fc57d7749edee585a50602f@ut.ac.ir> <8573002.CDJkKcVGEf@agathebauer> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart1834978.usQuhbGJ8B"; micalg="sha256"; protocol="application/pkcs7-signature" Sender: linux-trace-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-trace-users@vger.kernel.org --nextPart1834978.usQuhbGJ8B Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="iso-8859-1" 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 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= =20 running into or not: Try to see if you see the problem when you sample with= out=20 `ppp`. If not, then you can be pretty sure it's this issue. If you still se= e=20 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 hardw= are=20 and software. We would need something completely different to "fix" this, i= =2Ee.=20 something like a deeper LBR. That's btw another alternative you could try:= =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 always fa= r=20 too short and thus not practical to use in reality. Cheers =2D-=20 Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer KDAB (Deutschland) GmbH, a KDAB Group company Tel: +49-30-521325470 KDAB - The Qt, C++ and OpenGL Experts --nextPart1834978.usQuhbGJ8B Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCDEIw ggXmMIIDzqADAgECAhBqm+E4O/8ra58B1dm4p1JWMA0GCSqGSIb3DQEBDAUAMIGFMQswCQYDVQQG EwJHQjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYD VQQKExFDT01PRE8gQ0EgTGltaXRlZDErMCkGA1UEAxMiQ09NT0RPIFJTQSBDZXJ0aWZpY2F0aW9u IEF1dGhvcml0eTAeFw0xMzAxMTAwMDAwMDBaFw0yODAxMDkyMzU5NTlaMIGXMQswCQYDVQQGEwJH QjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYDVQQK ExFDT01PRE8gQ0EgTGltaXRlZDE9MDsGA1UEAxM0Q09NT0RPIFJTQSBDbGllbnQgQXV0aGVudGlj YXRpb24gYW5kIFNlY3VyZSBFbWFpbCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEB 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