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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 18682C46462 for ; Sun, 29 Jul 2018 17:06:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A8F0C20857 for ; Sun, 29 Jul 2018 17:06:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A8F0C20857 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726524AbeG2ShE (ORCPT ); Sun, 29 Jul 2018 14:37:04 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:34686 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726417AbeG2ShE (ORCPT ); Sun, 29 Jul 2018 14:37:04 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 262FD87A70; Sun, 29 Jul 2018 17:05:59 +0000 (UTC) Received: from krava (ovpn-204-74.brq.redhat.com [10.40.204.74]) by smtp.corp.redhat.com (Postfix) with SMTP id BF6222156701; Sun, 29 Jul 2018 17:05:56 +0000 (UTC) Date: Sun, 29 Jul 2018 19:05:56 +0200 From: Jiri Olsa To: Arnaldo Carvalho de Melo Cc: rodia@autistici.org, Jiri Olsa , lkml , Ingo Molnar , Namhyung Kim , David Ahern , Alexander Shishkin , Peter Zijlstra , Joe Mario Subject: Re: [PATCH] perf c2c report: Fix crash for empty browser Message-ID: <20180729170556.GB17776@krava> References: <20180724062008.26126-1-jolsa@kernel.org> <20180726193046.GC20438@kernel.org> <20180727070623.GA24770@krava> <20180727141340.GA4722@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180727141340.GA4722@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Sun, 29 Jul 2018 17:05:59 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Sun, 29 Jul 2018 17:05:59 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'jolsa@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 27, 2018 at 11:13:40AM -0300, Arnaldo Carvalho de Melo wrote: > Adding Joe to the CC list. > > Em Fri, Jul 27, 2018 at 09:06:23AM +0200, Jiri Olsa escreveu: > > On Thu, Jul 26, 2018 at 11:31:34PM +0000, rodia@autistici.org wrote: > > > On 2018-07-26 19:30, Arnaldo Carvalho de Melo wrote: > > > > Em Tue, Jul 24, 2018 at 08:20:08AM +0200, Jiri Olsa escreveu: > > > > > Do not try to display entry details if there's > > > > > not any. Currently this ends up in crash: > > > > > $ perf c2c report > > > > > perf: Segmentation fault > > > > > How to replicate this? > > > > > I tried: > > > > > $ perf record sleep 1 > > > > $ perf c2c report > > > > > But it didn't segfault > > > > Similarly I have tried : > > > $ perf record sleep 1 > > > $ perf c2c report > > > Then Press `d` to show the cache-line contents. > > > yep, sry I forgot to mention you need to press the 'd' to show details > > > > This replies the segfault on my machine (4.17.8-1). > > > The patch mentioned above should solve it, even tough I am not sure as I > > > haven't been able to recompile the kernel. > > > no need to recompile kernel > > > > The segfault by itself seems to be due to the report logic, as it did not > > > expect to report on an empty browser. > > > What has stepped me back is that application which I have been testing with > > > rely on multiple threads instantiated through pthread, which should be > > > counted in user-level threads right? But they still seem to return an empty > > > browser. > > > right, c2c scans read/write accesses and tries to find false sharing > > cases maybe there was nothing to be found > > > > When instead c2c is runned system-wide, with an application running on > > > multiple threads like firefox or julia, cache hits are measured and also > > > they are traced back in the source code. > > > I got a cache line (attached) for 'perf bench sched messaging' > > NOT being traced system wide and just for user (you'll get plenty > > of detected cachelines in kernel space): > > With that info in mind, we get: > > [root@seventh ~]# perf record sleep 1 > [ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0.001 MB perf.data (6 samples) ] > [root@seventh ~]# > [root@seventh ~]# > [root@seventh ~]# perf c2c report # and press 'd' > perf: Segmentation fault > -------- backtrace -------- > perf[0x5b1d2a] > /lib64/libc.so.6(+0x346df)[0x7fcb566e36df] > perf[0x46fcae] > perf[0x4a9f1e] > perf[0x4aa220] > perf(main+0x301)[0x42c561] > /lib64/libc.so.6(__libc_start_main+0xe9)[0x7fcb566cff29] > perf(_start+0x29)[0x42c999] > [root@seventh ~]# > > With your patches the segfault is gone, but I'd do a follow up patch to > show some message telling the user why 'd' showed nothing and > instructing him about what is missing, i.e. is this done on a perf.data > file that has no events of interest? Suggest using 'perf c2c record' or > 'perf record -e events,of,interest,to,perf,c2c', was this done on some > workload where no false sharing was detected? Say so, etc. ok, will try to come up with something > > I applied your patch with a more detailed commit log to state how this > can reproduced, etc, as usual: > > https://git.kernel.org/acme/c/983eb6aa7098 I checked, looks good, thanks jirka