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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 02B19C6786F for ; Thu, 1 Nov 2018 11:16:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C72AE2081B for ; Thu, 1 Nov 2018 11:16:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C72AE2081B 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 S1728150AbeKAUTL (ORCPT ); Thu, 1 Nov 2018 16:19:11 -0400 Received: from foss.arm.com ([217.140.101.70]:55026 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727736AbeKAUTL (ORCPT ); Thu, 1 Nov 2018 16:19:11 -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 98861A78; Thu, 1 Nov 2018 04:16:41 -0700 (PDT) Received: from [10.1.194.37] (e113632-lin.cambridge.arm.com [10.1.194.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4AA0D3F71D; Thu, 1 Nov 2018 04:16:39 -0700 (PDT) Subject: Re: [PATCH 07/10] sched/fair: Provide can_migrate_task_llc To: Peter Zijlstra Cc: Steven Sistare , mingo@redhat.com, subhra.mazumdar@oracle.com, dhaval.giani@oracle.com, rohit.k.jain@oracle.com, daniel.m.jordan@oracle.com, pavel.tatashin@microsoft.com, matt@codeblueprint.co.uk, umgwanakikbuti@gmail.com, riel@redhat.com, jbacik@fb.com, juri.lelli@redhat.com, linux-kernel@vger.kernel.org References: <1540220381-424433-1-git-send-email-steven.sistare@oracle.com> <1540220381-424433-8-git-send-email-steven.sistare@oracle.com> <20181031191459.GA3141@hirez.programming.kicks-ass.net> From: Valentin Schneider Message-ID: <10491016-9eec-846f-9632-f6de965508b6@arm.com> Date: Thu, 1 Nov 2018 11:16:37 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181031191459.GA3141@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 31/10/2018 19:14, Peter Zijlstra wrote: > On Mon, Oct 29, 2018 at 07:34:50PM +0000, Valentin Schneider wrote: >> On a sidenote, I find it a bit odd that the exec_start threshold depends on >> sysctl_sched_migration_cost, which to me is more about idle_balance() cost >> than "how long does it take for a previously run task to go cache cold". > > A long long (think 2.6.20 long ago) there was code that did boot-time > measurement of the various cache topology costs and that threshold was > related to that. > > That code got killed because of boot to boot variance and dubious > benefits. > > The migration cost is what it was replaced with as a single measure. > > migration cost was then later abused in the newidle balance because it > was over eager. Thanks! I tried following the blame rabbit hole but got a bit lost along the way. > Ideally we'd get rid of it there, because we've now got > that much more elaborate accounting, but Rohit tried and found some > regression because of that. > > Maybe we should remove it from newidle anyway. > Well, if we ditch idle_balance() in favor of stealing, that would "solve" it...