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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 E337FC43142 for ; Thu, 2 Aug 2018 13:19:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 99FE22150E for ; Thu, 2 Aug 2018 13:19:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 99FE22150E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732521AbeHBPKL (ORCPT ); Thu, 2 Aug 2018 11:10:11 -0400 Received: from foss.arm.com ([217.140.101.70]:58088 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732270AbeHBPKL (ORCPT ); Thu, 2 Aug 2018 11:10:11 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1C0707A9; Thu, 2 Aug 2018 06:19:00 -0700 (PDT) Received: from queper01-lin (queper01-lin.emea.arm.com [10.4.13.27]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 277BC3F2EA; Thu, 2 Aug 2018 06:18:56 -0700 (PDT) Date: Thu, 2 Aug 2018 14:18:51 +0100 From: Quentin Perret To: Peter Zijlstra Cc: rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, gregkh@linuxfoundation.org, mingo@redhat.com, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, patrick.bellasi@arm.com, valentin.schneider@arm.com, vincent.guittot@linaro.org, thara.gopinath@linaro.org, viresh.kumar@linaro.org, tkjos@google.com, joel@joelfernandes.org, smuckle@google.com, adharmap@quicinc.com, skannan@quicinc.com, pkondeti@codeaurora.org, juri.lelli@redhat.com, edubezval@gmail.com, srinivas.pandruvada@linux.intel.com, currojerez@riseup.net, javi.merino@kernel.org Subject: Re: [PATCH v5 09/14] sched: Add over-utilization/tipping point indicator Message-ID: <20180802131849.mqpt5lbtcqrxbwig@queper01-lin> References: <20180724122521.22109-1-quentin.perret@arm.com> <20180724122521.22109-10-quentin.perret@arm.com> <20180802122629.GU2476@hirez.programming.kicks-ass.net> <20180802130337.uf6tlac2hg4nkbwr@queper01-lin> <20180802130801.GL2494@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180802130801.GL2494@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday 02 Aug 2018 at 15:08:01 (+0200), Peter Zijlstra wrote: > On Thu, Aug 02, 2018 at 02:03:38PM +0100, Quentin Perret wrote: > > On Thursday 02 Aug 2018 at 14:26:29 (+0200), Peter Zijlstra wrote: > > > On Tue, Jul 24, 2018 at 01:25:16PM +0100, Quentin Perret wrote: > > > > @@ -5100,8 +5118,17 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) > > > > update_cfs_group(se); > > > > } > > > > > > > > - if (!se) > > > > + if (!se) { > > > > add_nr_running(rq, 1); > > > > + /* > > > > + * The utilization of a new task is 'wrong' so wait for it > > > > + * to build some utilization history before trying to detect > > > > + * the overutilized flag. > > > > + */ > > > > + if (flags & ENQUEUE_WAKEUP) > > > > + update_overutilized_status(rq); > > > > + > > > > + } > > > > > > > > hrtick_update(rq); > > > > } > > > > > > That is a somewhat dodgy hack. There is no guarantee what so ever that > > > when the task wakes next its history is any better. The comment doesn't > > > reflect this I feel. > > > > AFAICT the main use-case here is to avoid re-enabling the load balance > > and ruining all the task placement because of a tiny task. I don't > > really see how we can do that differently ... > > Sure I realize that.. but it doesn't completely avoid it. Suppose this > new task instantly blocks and wakes up again. Then its util signal will > be exactly what you didn't want but we'll account it and cause the above > scenario you wanted to avoid. That is true. ... I also realize now that this patch was written long before util_est, and that also has an impact here, especially in the scenario you described where the task blocks. So any wake-up after the first enqueue will risk to overutilize the system, even if the task blocked for ages. Hmm ...