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=-5.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 93828C169C4 for ; Mon, 11 Feb 2019 09:30:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9B56620823 for ; Mon, 11 Feb 2019 09:30:21 +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="AgdX6hXE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726243AbfBKJaT (ORCPT ); Mon, 11 Feb 2019 04:30:19 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:39274 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725986AbfBKJaT (ORCPT ); Mon, 11 Feb 2019 04:30:19 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=aKRhkuXk46b93kwjrTxIMTwquIkphDB1CHjLoQSZ7/M=; b=AgdX6hXEyJCeHJ8ctqbXXPTIf DvJ/dm9U5KVxP/bzrjn9D4bCfmRhUNiQmesq3wXdELrpawGqsLZFW07VKJbyj3uAmVkVHfPHj9zSt YORsu6U7GozBztG26JBoE9Gb6qPVwRUOhEuBuy5f6Rx/7UkD2MSA5+qacvt/LimCwf6MphyRKj1Hx u5SPclEY7XbR3Q/g94ZyDll9YLQyjj6CFegkqsCGSkCVA3CwRkKYlu6dCSg7omeV3FOi7UheIJONa uA0nCpApBPVonJv5ep50GIJZiOqIlmoSIhs8cZNX/O+gMIEPcSiGY105QKeRHtiItO3QGKK4BqlwW t8y4GpObg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gt7us-0005FV-0v; Mon, 11 Feb 2019 09:30:18 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E6E9321A7CCE6; Mon, 11 Feb 2019 10:30:14 +0100 (CET) Date: Mon, 11 Feb 2019 10:30:14 +0100 From: Peter Zijlstra To: Viresh Kumar Cc: Ingo Molnar , Vincent Guittot , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] sched/fair: Improve the for loop in select_idle_core() Message-ID: <20190211093014.GS32511@hirez.programming.kicks-ass.net> References: <6b165676325a47d67e667582a7b78da85c5c118a.1549536337.git.viresh.kumar@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6b165676325a47d67e667582a7b78da85c5c118a.1549536337.git.viresh.kumar@linaro.org> 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 Thu, Feb 07, 2019 at 04:16:06PM +0530, Viresh Kumar wrote: > @@ -6081,10 +6082,14 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int > for_each_cpu_wrap(core, cpus, target) { > bool idle = true; > > - for_each_cpu(cpu, cpu_smt_mask(core)) { > - cpumask_clear_cpu(cpu, cpus); > - if (!available_idle_cpu(cpu)) > + smt = cpu_smt_mask(core); > + cpumask_andnot(cpus, cpus, smt); So where the previous code was like 1-2 stores, you just added 16. (assuming 64bit and NR_CPUS=1024) And we still do the iteration anyway: > + for_each_cpu(cpu, smt) { > + if (!available_idle_cpu(cpu)) { > idle = false; > + break; > + } > } An actual improvement would've been: diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 38d4669aa2ef..2d352d6d15c7 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6082,7 +6082,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int bool idle = true; for_each_cpu(cpu, cpu_smt_mask(core)) { - cpumask_clear_cpu(cpu, cpus); + __cpumask_clear_cpu(cpu, cpus); if (!available_idle_cpu(cpu)) idle = false; }