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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 6A023C2BC61 for ; Mon, 29 Oct 2018 14:33:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2BEB120870 for ; Mon, 29 Oct 2018 14:33:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2BEB120870 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.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 S1726903AbeJ2XWD (ORCPT ); Mon, 29 Oct 2018 19:22:03 -0400 Received: from mga17.intel.com ([192.55.52.151]:60947 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725989AbeJ2XWD (ORCPT ); Mon, 29 Oct 2018 19:22:03 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 29 Oct 2018 07:33:09 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,440,1534834800"; d="scan'208";a="82434865" Received: from linux.intel.com ([10.54.29.200]) by fmsmga008.fm.intel.com with ESMTP; 29 Oct 2018 07:33:09 -0700 Received: from [10.251.20.185] (kliang2-mobl1.ccr.corp.intel.com [10.251.20.185]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by linux.intel.com (Postfix) with ESMTPS id 3CF1B58037D; Mon, 29 Oct 2018 07:33:08 -0700 (PDT) Subject: Re: [PATCHES/RFC] Re: A concern about overflow ring buffer mode To: Arnaldo Carvalho de Melo Cc: David Miller , linux-kernel@vger.kernel.org, Wang Nan , Jiri Olsa , Namhyung Kim , Kan Liang , Andi Kleen , Jin Yao , Peter Zijlstra References: <20181026.104513.2239058788450235574.davem@davemloft.net> <20181026183805.GD3353@kernel.org> <20181026184255.GE3353@kernel.org> <20181026190211.GF3353@kernel.org> <3b81c999-9039-94e9-7a74-cdbd48fca08b@linux.intel.com> <20181026191231.GG3353@kernel.org> <65cbd052-15d9-f3fb-4a8f-781c3ce7a297@linux.intel.com> <20181026192424.GH3353@kernel.org> <4f84468f-37d9-cf1b-12c1-514ef74b6a48@linux.intel.com> <20181029130331.GC21857@kernel.org> From: "Liang, Kan" Message-ID: <0247fca0-5a94-9a83-cefa-282804316729@linux.intel.com> Date: Mon, 29 Oct 2018 10:33:06 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181029130331.GC21857@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/29/2018 9:03 AM, Arnaldo Carvalho de Melo wrote: > Em Fri, Oct 26, 2018 at 04:11:51PM -0400, Liang, Kan escreveu: >> On 10/26/2018 3:24 PM, Arnaldo Carvalho de Melo wrote: >>> Em Fri, Oct 26, 2018 at 03:16:29PM -0400, Liang, Kan escreveu: >>>> On 10/26/2018 3:12 PM, Arnaldo Carvalho de Melo wrote: >>>>> Em Fri, Oct 26, 2018 at 03:07:40PM -0400, Liang, Kan escreveu: >>>>>> On 10/26/2018 3:02 PM, Arnaldo Carvalho de Melo wrote: >>>>> I checked and both have the same result. But I still think there is >>>>> value in having the shorter form, ok? > >>>> Sure. > >>> Ok. > >>> I think that we should default back to --no-overwrite till we get this >>> sorted out, as the effect is easily noticeable, as David reported and I >>> reproduced, when doing kernel builds. > >> It is mainly for performance reason to switch to overwrite mode. The impact >> was very small when I did my test. But now the effect is easily noticeable >> in other tests. Yes, I agree. We may change it back to non-overwrite mode >> until the issue is addressed. > > So, I have these two patches in my perf/core branch, with Fixes tags > that will make them get to the stable kernels, ok? I just realized that the problem in KNL will be back if we switch back to non-overwrite mode. The problem is that users have to wait tens of minutes to see perf top results on the screen in KNL. Before that, there is nothing but a black screen. Sorry I didn't notice it last Friday. Because I thought the ui_warning in perf_top__mmap_read() can give user a hint. So the user can switch to overwrite mode manually. But unfortunately, the ui_warning doesn't work. Because it is called after perf_top__mmap_read(). The processing time of perf_top__mmap_read() could be tens of minutes. Thanks, Kan > > > From f54ef0e7342efb77205b2faaacbcb81cdd31f064 Mon Sep 17 00:00:00 2001 > From: Arnaldo Carvalho de Melo > Date: Fri, 26 Oct 2018 15:55:23 -0300 > Subject: [PATCH 1/2] perf top: Allow disabling the overwrite mode > > In ebebbf082357 ("perf top: Switch default mode to overwrite mode") we > forgot to leave a way to disable that new default, add a --overwrite > option that can be disabled using --no-overwrite, since the code already > in such a way that we can readily disable this mode. > > This is useful when investigating bugs with this mode like the recent > report from David Miller where lots of unknown symbols appear due to > disabling the events while processing them which disables all record > types, not just PERF_RECORD_SAMPLE, which makes it impossible to resolve > maps when we lose PERF_RECORD_MMAP records. > > This can be easily seen while building a kernel, when there are lots of > short lived processes. > > Reported-by: David Miller > Acked-by: Kan Liang > Cc: Adrian Hunter > Cc: Andi Kleen > Cc: David Ahern > Cc: Jin Yao > Cc: Jiri Olsa > Cc: Namhyung Kim > Cc: Peter Zijlstra > Cc: Wang Nan > Fixes: ebebbf082357 ("perf top: Switch default mode to overwrite mode") > Link: https://lkml.kernel.org/n/tip-oqgsz2bq4kgrnnajrafcdhie@git.kernel.org > Signed-off-by: Arnaldo Carvalho de Melo > --- > tools/perf/Documentation/perf-top.txt | 5 +++++ > tools/perf/builtin-top.c | 2 ++ > 2 files changed, 7 insertions(+) > > diff --git a/tools/perf/Documentation/perf-top.txt b/tools/perf/Documentation/perf-top.txt > index 114fda12aa49..d4be6061fe1c 100644 > --- a/tools/perf/Documentation/perf-top.txt > +++ b/tools/perf/Documentation/perf-top.txt > @@ -242,6 +242,11 @@ Default is to monitor all CPUS. > --hierarchy:: > Enable hierarchy output. > > +--overwrite:: > + This is the default, but for investigating problems with it or any other strange > + behaviour like lots of unknown samples, we may want to disable this mode by using > + --no-overwrite. > + > --force:: > Don't do ownership validation. > > diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c > index d21d8751e749..214fad747b04 100644 > --- a/tools/perf/builtin-top.c > +++ b/tools/perf/builtin-top.c > @@ -1372,6 +1372,8 @@ int cmd_top(int argc, const char **argv) > "Show raw trace event output (do not use print fmt or plugins)"), > OPT_BOOLEAN(0, "hierarchy", &symbol_conf.report_hierarchy, > "Show entries in a hierarchy"), > + OPT_BOOLEAN(0, "overwrite", &top.record_opts.overwrite, > + "Use a backward ring buffer, default: yes"), > OPT_BOOLEAN(0, "force", &symbol_conf.force, "don't complain, do it"), > OPT_UINTEGER(0, "num-thread-synthesize", &top.nr_threads_synthesize, > "number of thread to run event synthesize"), >