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 52B0EC43603 for ; Thu, 12 Dec 2019 15:04:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2437C2054F for ; Thu, 12 Dec 2019 15:04:37 +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="Qk+JfLLq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728818AbfLLPEg (ORCPT ); Thu, 12 Dec 2019 10:04:36 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:59264 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728624AbfLLPEg (ORCPT ); Thu, 12 Dec 2019 10:04:36 -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=rnKPEPHq5zWJRr2D9M8D7b1LZbRScvFVrRnHqxj8R2Y=; b=Qk+JfLLq7VE+GfWfLz9sBZPDG RbfdAD7UVvPSwk+5qsrwzipk3m6cYByNZmYuaEZDxb186BGsGu3DzU5KQzhPiTSNujtPXM8IP5/uS 996MttNeOxiAldY20deJCtPv6xa+LrcH+bbOlxznh0H0//johEHSu0frJ4N5Et3Cd74LKWfWp3T+s FsnylRaDG6sDaEghhqcx7mSzQ9CnwZtYvJ6DJS8yy/X9Yg4CMtndj+OuPOOHad5DBt4nB13KYb/UO V9t4f6VmybuDBuc1lgmBFe60y3GDRIgYr7Xm5ln1dac6hpLOrsUE/qWrythI3Y/oriSkR/SQ/Z1wM w4Yfqghnw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1ifQ11-0000oE-Pv; Thu, 12 Dec 2019 15:04:31 +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 29CB4304D2B; Thu, 12 Dec 2019 16:03:09 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9053920120E34; Thu, 12 Dec 2019 16:04:29 +0100 (CET) Date: Thu, 12 Dec 2019 16:04:29 +0100 From: Peter Zijlstra To: Cheng Jian Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, chenwandun@huawei.com, xiexiuqi@huawei.com, liwei391@huawei.com, huawei.libin@huawei.com, bobo.shaobowang@huawei.com, juri.lelli@redhat.com, vincent.guittot@linaro.org Subject: Re: [PATCH] sched/fair: Optimize select_idle_cpu Message-ID: <20191212150429.GZ2827@hirez.programming.kicks-ass.net> References: <20191212144102.181510-1-cj.chengjian@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191212144102.181510-1-cj.chengjian@huawei.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 Thu, Dec 12, 2019 at 10:41:02PM +0800, Cheng Jian wrote: > select_idle_cpu will scan the LLC domain for idle CPUs, > it's always expensive. so commit > 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()") > introduces a way to limit how many CPUs we scan. > > But this also lead to the following issue: > > Our threads are all bind to the front CPUs of the LLC domain, > and now all the threads runs on the last CPU of them. nr is > always less than the cpumask_weight, for_each_cpu_wrap can't > find the CPU which our threads can run on, so the threads stay > at the last CPU all the time. > > Fixes: 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()") > Signed-off-by: Cheng Jian > --- > kernel/sched/fair.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 08a233e97a01..16a29b570803 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5834,6 +5834,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t > s64 delta; > int this = smp_processor_id(); > int cpu, nr = INT_MAX, si_cpu = -1; > + struct cpumask cpus; NAK, you must not put a cpumask on stack.