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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 90B5AC10DCE for ; Fri, 13 Mar 2020 10:26:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E7F420746 for ; Fri, 13 Mar 2020 10:26:40 +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="ffp0mdh2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726643AbgCMK0j (ORCPT ); Fri, 13 Mar 2020 06:26:39 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:35204 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726364AbgCMK0j (ORCPT ); Fri, 13 Mar 2020 06:26:39 -0400 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; bh=w0wh3Bo/E+yd8WLbN+yv3HuUw/Fwj4zAqX3kGWsq99k=; b=ffp0mdh20NmxHjh2w/JzrVfCQI mu3bjvWBkQPZQXWLzqkoqKY7m6Qj7J52aXZVzMkS00trEJ6UBIkV8TuIMkGSgyBEfEKiGnWnlQ6NY Od6OOHdBPZ/blRIwjrgOnzRxCwfPJQydWH6Eyyik6yeMJTMfv5nfTueGHwIWv8kku4auV5xPrIr2K ZjVarp6wWK/7GFhQXBn1/jvLkLqJ8PD7wHQR97eUDEgIOsQgaHEhasMs7iw2ew6bEWxdnJITTa2DC uWcxpvtJUSOsu6j74Q0XIIpn311k6OAVsRdZC1iLsZFFyVWzBrms9lornLP24UkfkhYQzRohGhLzi TcdlVcQQ==; 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 1jChWP-0001OU-Bf; Fri, 13 Mar 2020 10:26:29 +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 490D1305F2E; Fri, 13 Mar 2020 11:26:27 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E8430214344F4; Fri, 13 Mar 2020 11:26:26 +0100 (CET) Date: Fri, 13 Mar 2020 11:26:26 +0100 From: Peter Zijlstra To: Vincent Guittot Cc: mingo@redhat.com, juri.lelli@redhat.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched/fair: improve spreading of utilization Message-ID: <20200313102626.GY12561@hirez.programming.kicks-ass.net> References: <20200312165429.990-1-vincent.guittot@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200312165429.990-1-vincent.guittot@linaro.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 12, 2020 at 05:54:29PM +0100, Vincent Guittot wrote: > During load_balancing, a group with spare capacity will try to pull some > utilizations from an overloaded group. In such case, the load balance > looks for the runqueue with the highest utilization. Nevertheless, it > should also ensure that there are some pending tasks to pull otherwise > the load balance will fail to pull a task and the spread of the load will > be delayed. > > This situation is quite transient but it's possible to highlight the > effect with a short run of sysbench test so the time to spread task impacts > the global result significantly. > > Below are the average results for 15 iterations on an arm64 octo core: > sysbench --test=cpu --num-threads=8 --max-requests=1000 run > > tip/sched/core +patchset > total time: 172ms 158ms > per-request statistics: > avg: 1.337ms 1.244ms > max: 21.191ms 10.753ms > > The average max doesn't fully reflect the wide spread of the value which > ranges from 1.350ms to more than 41ms for the tip/sched/core and from > 1.350ms to 21ms with the patch. > > Other factors like waiting for an idle load balance or cache hotness > can delay the spreading of the tasks which explains why we can still > have up to 21ms with the patch. Thanks!