From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757368AbcASHme (ORCPT ); Tue, 19 Jan 2016 02:42:34 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49050 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751409AbcASHmb (ORCPT ); Tue, 19 Jan 2016 02:42:31 -0500 Date: Tue, 19 Jan 2016 08:42:28 +0100 From: Jiri Olsa To: Mel Gorman Cc: Jiri Olsa , Arnaldo Carvalho de Melo , LKML Subject: Re: perf stat stddev reporting broken since "perf stat: Introduce read_counters function" Message-ID: <20160119074228.GB20358@krava.brq.redhat.com> References: <20160118175946.GC10802@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160118175946.GC10802@techsingularity.net> 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 On Mon, Jan 18, 2016 at 05:59:46PM +0000, Mel Gorman wrote: > I noticed that perf stat in 4.4 is not printing stddev figures as > expected and bisected it to commit 106a94a0f8c2 ("perf stat: Introduce > read_counters function"). > > # Kernel 4.4 > # make clean && make prefix=/usr && ./perf stat -r 5 sleep 1 > Performance counter stats for 'sleep 1' (5 runs): > > 0.466683 task-clock (msec) # 0.000 CPUs utilized > 1 context-switches # 0.002 M/sec > 1 cpu-migrations # 0.002 M/sec > 66 page-faults # 0.144 M/sec > 1,630,220 cycles # 3.562 GHz > stalled-cycles-frontend > stalled-cycles-backend > 902,686 instructions # 0.66 insns per cycle > 185,692 branches # 405.786 M/sec > 8,640 branch-misses # 4.63% of all branches > > 1.000855883 seconds time elapsed ( +- 0.01% ) > > # git checkout 106a94a0f8c207ef4113ce7e32f34a00b3b174e7^ > Performance counter stats for 'sleep 1' (5 runs): > > 0.397939 task-clock (msec) # 0.000 CPUs utilized ( +- 3.37% ) > 1 context-switches # 0.003 M/sec > 0 cpu-migrations # 0.000 K/sec > 67 page-faults # 0.169 M/sec ( +- 0.56% ) > 1,360,763 cycles # 3.420 GHz ( +- 2.14% ) > stalled-cycles-frontend > stalled-cycles-backend > 903,901 instructions # 0.66 insns per cycle ( +- 0.24% ) > 186,472 branches # 468.595 M/sec ( +- 0.29% ) > 8,599 branch-misses # 4.61% of all branches ( +- 0.77% ) > > 1.000761882 seconds time elapsed ( +- 0.00% ) > > # git checkout 106a94a0f8c207ef4113ce7e32f34a00b3b174e7 > > Performance counter stats for 'sleep 1' (5 runs): > > 0.583178 task-clock (msec) # 0.001 CPUs utilized > 1 context-switches # 0.002 M/sec > 0 cpu-migrations # 0.000 K/sec > 67 page-faults # 0.141 M/sec > 1,224,416 cycles # 2.585 GHz > stalled-cycles-frontend > stalled-cycles-backend > 892,568 instructions # 0.68 insns per cycle > 184,975 branches # 390.554 M/sec > 8,512 branch-misses # 4.57% of all branches > > 1.000889249 seconds time elapsed ( +- 0.01% ) > > I checked and current master in Linus' tree is also broken. Is this > change in documented perf stat behaviour intentional? nope, not intentional.. I'll check on that, thanks for reporting jirka