From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752460Ab3KRNZZ (ORCPT ); Mon, 18 Nov 2013 08:25:25 -0500 Received: from mx1.redhat.com ([209.132.183.28]:3308 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751971Ab3KRNZS (ORCPT ); Mon, 18 Nov 2013 08:25:18 -0500 Date: Mon, 18 Nov 2013 14:25:10 +0100 From: Jiri Olsa To: Arnaldo Carvalho de Melo Cc: Ingo Molnar , David Ahern , linux-kernel@vger.kernel.org, Frederic Weisbecker , Namhyung Kim Subject: Re: [PATCH] perf top: Make -g refer to callchains Message-ID: <20131118132510.GB24375@krava.brq.redhat.com> References: <1384487490-6865-1-git-send-email-dsahern@gmail.com> <20131115054609.GB4514@gmail.com> <20131118125945.GA3669@ghostprotocols.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131118125945.GA3669@ghostprotocols.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 18, 2013 at 09:59:45AM -0300, Arnaldo Carvalho de Melo wrote: > Em Fri, Nov 15, 2013 at 06:46:09AM +0100, Ingo Molnar escreveu: > > btw., here's some 'perf top' call graph performance and profiling > > quality feedback, with the latest perf code: > > > > 'perf top --call-graph fp' now works very well, using just 0.2% > > of CPU time on a fast system: > > > > 4676 mingo 20 0 612m 56m 9948 S 1 0.2 0:00.68 perf > > > > 'perf top --call-graph dwarf' on the other hand is horrendously > > slow, using 20% of CPU time on a 4 GHz CPU: > > > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > > 4646 mingo 20 0 658m 81m 12m R 19 0.3 0:18.17 perf > > > > On another system with a 2.4GHz CPU it's taking up 100% of CPU > > time (!): > > > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > > 8018 mingo 20 0 290320 45220 8520 R 99.5 0.3 0:58.81 perf > > > > Profiling 'perf top' shows all sorts of very high dwarf > > processing overhead: > > Yeah, top dwarf callchain has been so far a proof of concept, it > exacerbates problems that can be seen on 'report', but since its live, > we can see it more clearly. > > The work on improving callchain processing, (rb_tree'ing, new comm > infrastructure) alleviated the problem a bit. > > Tuning the stack size requested from the kernel and using --max-stack > can help when it is really needed, but yes, work on it is *badly* needed. agreed ;-) also there's new remote unwind interface recently added into libdw, which seems to be faster than libunwind. I plan on adding this soon. jirka