From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751988AbZL2CZR (ORCPT ); Mon, 28 Dec 2009 21:25:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751700AbZL2CZQ (ORCPT ); Mon, 28 Dec 2009 21:25:16 -0500 Received: from mga11.intel.com ([192.55.52.93]:41384 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751638AbZL2CZP (ORCPT ); Mon, 28 Dec 2009 21:25:15 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.47,465,1257148800"; d="scan'208";a="759788150" Subject: Re: tbench regression with 2.6.33-rc1 From: Lin Ming To: Mike Galbraith Cc: "peterz@infradead.org" , "mingo@elte.hu" , "tglx@linutronix.de" , linux-kernel , "Zhang, Yanmin" In-Reply-To: <1261902760.6201.33.camel@marge.simson.net> References: <1261739467.10685.18.camel@minggr.sh.intel.com> <1261902760.6201.33.camel@marge.simson.net> Content-Type: text/plain Date: Tue, 29 Dec 2009 10:09:42 +0800 Message-Id: <1262052582.10685.59.camel@minggr.sh.intel.com> Mime-Version: 1.0 X-Mailer: Evolution 2.24.1 (2.24.1-2.fc10) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2009-12-27 at 16:32 +0800, Mike Galbraith wrote: > On Fri, 2009-12-25 at 19:11 +0800, Lin Ming wrote: > > Hi, > > > > Test machine: 16 cpus (4P/2Core/HT), 8G mem > > tbench test command: > > tbench_srv & > > tbench 32 > > > > Compared with 2.6.32, tbench has ~4% regression in 2.6.33-rc1. > > > > >>From vmstat data, the context switch number also drop ~4%. > > perf top data does not show much differences. > > > > But lockstat data shows huge difference in rq->lock, as below. > > See the attachment for the full lockstat data. > > > > Any clue of this regression? > > Nope, but I see regression I haven't been able to identify as well. Hi, Mike More info here, I only saw regression on Tulsa machine. No regression on Nehalem core 2 machine. And also no regression if I run tbench with RT scheduler on tulsa machine, as below command, schedtool -R -p 20 -e tbench_srv & schedtool -R -p 20 -e tbench 32 So seems this regression is CFS scheduler related. I also did a lot of bisect, but the result was not stable. Looks like this regression was not caused by a single commit. Lin Ming > > Tbench state of the union according to my box below. > > With a max performance config, 32.2 is down ~4% vs 31.9, most of which > is doing affinity checks on every wakeup. That has it's benefits too, > but definitely ain't free, or even particularly cheap for fast movers. > Would be nice to find a way to keep the ramp-up improvements without > this much cost. > > Perf also isn't free, and in 33, we lost the ability to config it out, > but even doing so via axe, there's an unidentified regression. > > As usual, bisection of tbench variance was a wasted effort. > > 2.6.31.9 = -CONFIG_PERF_COUNTERS > 2.6.31.9p = +CONFIG_PERF_COUNTERS > 2.6.32.2 = -CONFIG_PERF_EVENTS > 2.6.32.2p = +CONFIG_PERF_EVENTS > git = v2.6.33-rc2 > tip = v2.6.33-rc1-306-gae7a88c > > tbench 8 > 2.6.31.9 1190 MB/sec > 2.6.31.9p 1172 MB/sec .984 > 2.6.32.2 1146 MB/sec .977 vs 31.9 .963 > 2.6.32.2p 1129 MB/sec .985 vs 31.9 .948 > 2.6.33.git 1117 MB/sec .989 vs 31.9 .938 > 2.6.33.tip 1121 MB/sec 1.003 vs 31.9 .942 > > 2.6.32.2 1146 MB/sec 1.000 > 2.6.32.2x 1181 MB/sec 1.030 vs 31.9 .992 > > 2.6.33.git 1117 MB/sec 1.000 > 2.6.33.gitx 1145 MB/sec 1.025 vs 32.2x .969 vs 31.9 .962 (perf/hwbp off via axe) > > 2.6.32.2x diff > diff --git a/kernel/sched.c b/kernel/sched.c > index d079a9f..b71cb91 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -2363,6 +2363,9 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, > orig_cpu = cpu; > > #ifdef CONFIG_SMP > + if (cpu == this_cpu) > + goto out_stats; > + > if (unlikely(task_running(rq, p))) > goto out_activate; > > @@ -2389,6 +2392,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, > WARN_ON(p->state != TASK_WAKING); > cpu = task_cpu(p); > > +out_stats: > #ifdef CONFIG_SCHEDSTATS > schedstat_inc(rq, ttwu_count); > if (cpu == this_cpu) > >