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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 06F9BC433ED for ; Fri, 7 May 2021 13:47:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA1F861104 for ; Fri, 7 May 2021 13:47:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235973AbhEGNsI (ORCPT ); Fri, 7 May 2021 09:48:08 -0400 Received: from foss.arm.com ([217.140.110.172]:59764 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234951AbhEGNsG (ORCPT ); Fri, 7 May 2021 09:48:06 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CFFFF106F; Fri, 7 May 2021 06:47:05 -0700 (PDT) Received: from e113632-lin (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5F8413F73B; Fri, 7 May 2021 06:47:04 -0700 (PDT) From: Valentin Schneider To: Vincent Guittot Cc: linux-kernel , Peter Zijlstra , Ingo Molnar , Dietmar Eggemann , Morten Rasmussen , Qais Yousef , Quentin Perret , Pavan Kondeti , Rik van Riel , Lingutla Chandrasekhar Subject: Re: [PATCH 2/2] sched/fair: Relax task_hot() for misfit tasks In-Reply-To: References: <20210415175846.494385-1-valentin.schneider@arm.com> <20210415175846.494385-3-valentin.schneider@arm.com> <20210416135113.GA16445@vingu-book> <87blaakxji.mognet@arm.com> <878s5bvrij.mognet@arm.com> Date: Fri, 07 May 2021 14:46:59 +0100 Message-ID: <87y2cqirl8.mognet@arm.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Vincent, apologies for the belated reply On 30/04/21 08:58, Vincent Guittot wrote: > On Wed, 21 Apr 2021 at 12:52, Valentin Schneider > wrote: >> On 20/04/21 16:33, Vincent Guittot wrote: >> > Is it something that happens often or just a sporadic/transient state >> > ? I mean does it really worth the extra complexity and do you see >> > performance improvement ? >> > >> >> "Unfortunately" yes, this is a relatively common scenario when running "1 >> big task per CPU" types of workloads. The expected behaviour for big.LITTLE >> systems is to upmigrate tasks stuck on the LITTLE CPUs as soon as a big CPU >> becomes free, usually via newidle balance (which, since they process work >> faster than the LITTLEs, is bound to happen), and an extra task being >> enqueued at "the wrong time" can prevent this from happening. >> >> This usually means a misfit task can take a few dozen extra ms than it > > A few dozens is quite long. With a big core being idle, it should try > every 8ms on a quad x quad system and I suspect the next try will be > during the next tick. Would be good to understand why it has to wait > so much > True, IIRC this was mostly due to a compound effect of the different issues I've described in that thread (and the previous one). Now that 9bcb959d05ee ("sched/fair: Ignore percpu threads for imbalance pulls") is in, I'll re-run some tests against upstream and see how we fare.