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_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 20102C47247 for ; Thu, 30 Apr 2020 13:56:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EEC2720870 for ; Thu, 30 Apr 2020 13:56:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728085AbgD3N4i (ORCPT ); Thu, 30 Apr 2020 09:56:38 -0400 Received: from foss.arm.com ([217.140.110.172]:55172 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728732AbgD3N4h (ORCPT ); Thu, 30 Apr 2020 09:56:37 -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 7F4691063; Thu, 30 Apr 2020 06:56:36 -0700 (PDT) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2DC263F68F; Thu, 30 Apr 2020 06:56:35 -0700 (PDT) References: <20200428050242.17717-1-swood@redhat.com> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Vincent Guittot Cc: Scott Wood , Steven Rostedt , Ingo Molnar , Peter Zijlstra , Dietmar Eggemann , Rik van Riel , Mel Gorman , linux-kernel , linux-rt-users Subject: Re: [RFC PATCH 0/3] newidle_balance() latency mitigation In-reply-to: Date: Thu, 30 Apr 2020 14:56:29 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On 30/04/20 13:42, Vincent Guittot wrote: >> >> Random thought that just occurred to me; in the grand scheme of things, >> >> with something in the same spirit as task-stealing (i.e. don't bother with >> >> a full fledged balance at newidle, just pick one spare task somewhere), >> >> none of this would be required. >> > >> > newly idle load balance already stops after picking 1 task >> >> Mph, I had already forgotten your changes there. Is that really always the >> case for newidle? In e.g. the busiest->group_type == group_fully_busy case, >> I think we can pull more than one task. > > for newly_idle load balance, detach_tasks stops after finding 1 suitable task > Right, I hadn't noticed 7e96fa5875d4 ("sched: pull only one task during NEWIDLE balancing to limit critical section") >> >> > Now if your proposal is to pick one random task on one random cpu, I'm >> > clearly not sure that's a good idea >> > >> >> IIRC Steve's implementation was to "simply" pull one task from any CPU >> within the LLC domain that had > 1 runnable tasks. I quite like this since >> picking any one task is almost always better than switching to the idle >> task, but it wasn't a complete newidle_balance() replacement just yet. >> >> > >> >> >> >> Sadly I don't think anyone has been looking at it any recently.