Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755856AbZD2GIu (ORCPT ); Wed, 29 Apr 2009 02:08:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752548AbZD2GIh (ORCPT ); Wed, 29 Apr 2009 02:08:37 -0400 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:40412 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752045AbZD2GIh (ORCPT ); Wed, 29 Apr 2009 02:08:37 -0400 From: KOSAKI Motohiro To: balbir@linux.vnet.ibm.com Subject: Re: [PATCH] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count Cc: kosaki.motohiro@jp.fujitsu.com, LKML , Bharata B Rao , Balaji Rao , Dhaval Giani , KAMEZAWA Hiroyuki , Peter Zijlstra , Ingo Molnar , Martin Schwidefsky , seto.hidetoshi@jp.fujitsu.com In-Reply-To: <20090429054453.GA789@balbir.in.ibm.com> References: <20090429111558.4B0B.A69D9226@jp.fujitsu.com> <20090429054453.GA789@balbir.in.ibm.com> Message-Id: <20090429150116.4B1A.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50 [ja] Date: Wed, 29 Apr 2009 15:08:34 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2358 Lines: 71 > > > This will make the end result very off the real value due to large > > > batch value per cpu. If we are going to go this route, we should > > > probably consider using __percpu_counter_sum so that the batch value > > > does not show data that is way off. > > > > No problem. > > > > end-user don't see cputime itself. they see converted time. > > cpuacct_stats_show() use cputime64_to_clock_t. it mean > > the value less than 10msec don't display. > > > > Yes, I know, I reviewed Bharata's patch and suggested converting to > clock_t for consistency with other metrics. Oh, sorry. I didn't know this. > > -------------------------------------------------------- > > static int cpuacct_stats_show(struct cgroup *cgrp, struct cftype *cft, > > struct cgroup_map_cb *cb) > > { > > struct cpuacct *ca = cgroup_ca(cgrp); > > int i; > > > > for (i = 0; i < CPUACCT_STAT_NSTATS; i++) { > > s64 val = percpu_counter_read(&ca->cpustat[i]); > > My point is, this should probably be percpu_counter_sum(), but that > can be expensive and we were willing to tollerate some inaccuracy due > to batch value, I think your patch adds to the inaccuracy even more, > even though it fixes a genuine problem. Not expensive. cpuacct_stats_show() is only called when reading stat file. it definitely slow-path. I think we can use percpu_counter_sum(). However, I doubt its worth. before my patch: VIRT_CPU_ACCOUNTING=y: accuracy but slow VIRT_CPU_ACCOUNTING=n: inaccuracy few tick but fast my patch VIRT_CPU_ACCOUNTING=y: inaccuracy few tick but fast VIRT_CPU_ACCOUNTING=n: inaccuracy few tick but fast if my inaccuracy is wrong, current code is also crap when VIRT_CPU_ACCOUNTING=n. I only make const accuracy to VIRT_CPU_ACCOUNTING=y and n. Thought? Although you still think percpu_counter_sum() is better, I can do it. > > > > val = cputime64_to_clock_t(val); > > cb->fill(cb, cpuacct_stat_desc[i], val); > > } > > return 0; > > } > > -------------------------------------------------------- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/