Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752776AbcDZV6P (ORCPT ); Tue, 26 Apr 2016 17:58:15 -0400 Received: from mail-wm0-f47.google.com ([74.125.82.47]:35986 "EHLO mail-wm0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752220AbcDZV6N (ORCPT ); Tue, 26 Apr 2016 17:58:13 -0400 Date: Tue, 26 Apr 2016 23:58:10 +0200 From: Frederic Weisbecker To: Arnaldo Carvalho de Melo Cc: Alexei Starovoitov , David Ahern , Peter Zijlstra , Ingo Molnar , Adrian Hunter , Brendan Gregg , Alexander Shishkin , Alexei Starovoitov , He Kuang , Jiri Olsa , Masami Hiramatsu , Milian Wolff , Namhyung Kim , Stephane Eranian , Thomas Gleixner , Vince Weaver , Wang Nan , Zefan Li , Linux Kernel Mailing List Subject: Re: [PATCH/RFC v3] perf core: Allow setting up max frame stack depth via sysctl Message-ID: <20160426215806.GA15680@lerouge> References: <20160422221806.GA62857@ast-mbp.thefacebook.com> <20160425161425.GA25218@kernel.org> <20160425162706.GB25218@kernel.org> <20160425192229.GC25218@kernel.org> <20160425200646.GA23875@ast-mbp.thefacebook.com> <20160425201750.GD25218@kernel.org> <20160425215947.GA25915@ast-mbp.thefacebook.com> <20160425234138.GA16708@kernel.org> <20160426000724.GA28705@ast-mbp.thefacebook.com> <20160426002928.GB16708@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160426002928.GB16708@kernel.org> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1848 Lines: 48 On Mon, Apr 25, 2016 at 09:29:28PM -0300, Arnaldo Carvalho de Melo wrote: > commit cd544af4f7fede01cb512d52bb3efe62aa19271d > Author: Arnaldo Carvalho de Melo > Date: Thu Apr 21 12:28:50 2016 -0300 > > perf core: Allow setting up max frame stack depth via sysctl > > The default remains 127, which is good for most cases, and not even hit > most of the time, but then for some cases, as reported by Brendan, 1024+ > deep frames are appearing on the radar for things like groovy, ruby. > > And in some workloads putting a _lower_ cap on this may make sense. One > that is per event still needs to be put in place tho. > > The new file is: > > # cat /proc/sys/kernel/perf_event_max_stack > 127 > > Chaging it: > > # echo 256 > /proc/sys/kernel/perf_event_max_stack > # cat /proc/sys/kernel/perf_event_max_stack > 256 > > But as soon as there is some event using callchains we get: > > # echo 512 > /proc/sys/kernel/perf_event_max_stack > -bash: echo: write error: Device or resource busy > # > > Because we only allocate the callchain percpu data structures when there > is a user, which allows for changing the max easily, its just a matter > of having no callchain users at that point. > > Reported-and-Tested-by: Brendan Gregg > Acked-by: Alexei Starovoitov > Acked-by: David Ahern Reviewed-by: Frederic Weisbecker I first thought that this should be a tunable per event instead of a global sysctl but then I realized that we still need a root-only-tunable maximum limit value to oppose against any future per event limit and this sysctl value does the job. Nice patch! Thanks.