From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966667Ab2EQV4y (ORCPT ); Thu, 17 May 2012 17:56:54 -0400 Received: from merlin.infradead.org ([205.233.59.134]:34935 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965954Ab2EQV4x convert rfc822-to-8bit (ORCPT ); Thu, 17 May 2012 17:56:53 -0400 Message-ID: <1337291805.4281.97.camel@twins> Subject: Re: [PATCH 1/2] lib: Proportions with flexible period From: Peter Zijlstra To: Jan Kara Cc: Wu Fengguang , LKML , linux-mm@kvack.org Date: Thu, 17 May 2012 23:56:45 +0200 In-Reply-To: <1337096583-6049-2-git-send-email-jack@suse.cz> References: <1337096583-6049-1-git-send-email-jack@suse.cz> <1337096583-6049-2-git-send-email-jack@suse.cz> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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..