From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 360F1C35679 for ; Mon, 24 Feb 2020 09:32:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EF44B20714 for ; Mon, 24 Feb 2020 09:32:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="pJxRw5xv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727197AbgBXJcd (ORCPT ); Mon, 24 Feb 2020 04:32:33 -0500 Received: from merlin.infradead.org ([205.233.59.134]:34982 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726452AbgBXJcd (ORCPT ); Mon, 24 Feb 2020 04:32:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=YE6seiuyITlCDuzDkVuYwXtaOchvz2Zcj5WBB7bLhu0=; b=pJxRw5xvyA192Np0aiMhypwZx5 6oXL9mvcpUosr3wV8H+J4Pe0XSbsDTfuIGe/lznJnmhRjC1QOh+svtG3exsfFw2TsiSD9nwLUauZh QyKAb45l6kxXSQnWG9VimZkphBY5F3R5hmB6oZPk3jLs7NFo57HiA+dR/p5iOSE7JMCMF+EoC2zHK ZO+9bHWYjD99JOZqewDCfXi812/xZHfqRRJYVXesmhmmBTFa3HSlfyFN7cSimQHbkSuhFPEjT1Qn3 yQIoiitPZYoT2vQCv5mc8c295Y2yPEWWU3wl4VKbhR/oId6VvceXkO12wCmV+KCqP/05N4ug7nGwb 6Ksxurig==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j6A66-0002rC-HM; Mon, 24 Feb 2020 09:32:18 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id D3696300F7A; Mon, 24 Feb 2020 10:30:20 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 59F282B4DAAD0; Mon, 24 Feb 2020 10:32:15 +0100 (CET) Date: Mon, 24 Feb 2020 10:32:15 +0100 From: Peter Zijlstra To: qiwuchen55@gmail.com Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, linux-kernel@vger.kernel.org, chenqiwu Subject: Re: [PATCH] sched/pelt: use shift operation instead of division operation Message-ID: <20200224093215.GC14897@hirez.programming.kicks-ass.net> References: <1582515055-14515-1-git-send-email-qiwuchen55@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1582515055-14515-1-git-send-email-qiwuchen55@gmail.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 24, 2020 at 11:30:55AM +0800, qiwuchen55@gmail.com wrote: > From: chenqiwu > > Use shift operation to calculate the periods instead of division, > since shift operation is more efficient than division operation. > > Signed-off-by: chenqiwu > --- > kernel/sched/pelt.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c > index bd006b7..ac79f8e 100644 > --- a/kernel/sched/pelt.c > +++ b/kernel/sched/pelt.c > @@ -114,7 +114,7 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3) > u64 periods; > > delta += sa->period_contrib; > - periods = delta / 1024; /* A period is 1024us (~1ms) */ > + periods = delta >> 10; /* A period is 1024us (~1ms) */ Find me a compiler that stupid.