From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753305Ab2EROmd (ORCPT ); Fri, 18 May 2012 10:42:33 -0400 Received: from cantor2.suse.de ([195.135.220.15]:45025 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750920Ab2EROmb (ORCPT ); Fri, 18 May 2012 10:42:31 -0400 Date: Fri, 18 May 2012 16:42:17 +0200 From: Jan Kara To: Peter Zijlstra Cc: Jan Kara , Wu Fengguang , LKML , linux-mm@kvack.org Subject: Re: [PATCH 1/2] lib: Proportions with flexible period Message-ID: <20120518144217.GC6875@quack.suse.cz> References: <1337096583-6049-1-git-send-email-jack@suse.cz> <1337096583-6049-2-git-send-email-jack@suse.cz> <1337291805.4281.97.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1337291805.4281.97.camel@twins> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 17-05-12 23:56:45, Peter Zijlstra wrote: > On Tue, 2012-05-15 at 17:43 +0200, Jan Kara wrote: > > +void fprop_fraction_percpu(struct fprop_global *p, > > + struct fprop_local_percpu *pl, > > + unsigned long *numerator, unsigned long *denominator) > > +{ > > + unsigned int seq; > > + s64 den; > > + > > + do { > > + seq = read_seqcount_begin(&p->sequence); > > + fprop_reflect_period_percpu(p, pl); > > + *numerator = percpu_counter_read_positive(&pl->events); > > + den = percpu_counter_read(&p->events); > > + if (den <= 0) > > + den = percpu_counter_sum(&p->events); > > + *denominator = den; > > + } while (read_seqcount_retry(&p->sequence, seq)); > > +} > > > why not use percpu_counter_read_positive(&p->events) and ditch > percpu_counter_sum()? That sum can be terribly expensive.. Yes. I'm actually not sure why I used the _sum here... Thanks for spotting this. Honza -- Jan Kara SUSE Labs, CR