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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 F0ADEC433DB for ; Fri, 8 Jan 2021 19:50:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 92CC523AA7 for ; Fri, 8 Jan 2021 19:50:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729034AbhAHTuu (ORCPT ); Fri, 8 Jan 2021 14:50:50 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48480 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727376AbhAHTuu (ORCPT ); Fri, 8 Jan 2021 14:50:50 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EC110C061380 for ; Fri, 8 Jan 2021 11:50:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=qGT6ITD948+X3O7N9PZkCxcWPjEhw3d7HZbLs1mJhIY=; b=N2XSu3XcfBvkwMqILWi8ee02XA lPHgG0nqqDqhy/RUGzSZFLYah/McTK5lgY6bCENRaZzFPvstaoxC6Qj08YV5ss8f2VdAd3O1OaAC5 t5343BTxRxm2W1WDn1TobVJ2P09gjTDxUiw5OTFQu4ryujmPtIP6acpOti4MJW1hctIF4MGw6Ni0e Ap40m7rYxRw1jZ6wrKHJerRn0rtxp2KjVifO2AAqaOCE+8n4Krg/hJEtEJmYALDowiYv5qxG12u0I KXMvQN9DSMOEaFm+vv5h9PkWte1RXWuv6N3CU1Ca1dGpEb9E/J+nfesHwmeAB4Idew08OD6Tx3WQU /E2LFKkQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kxxlQ-0007r0-2L; Fri, 08 Jan 2021 19:49:36 +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 93C933003D8; Fri, 8 Jan 2021 20:49:33 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 82B842C48C575; Fri, 8 Jan 2021 20:49:33 +0100 (CET) Date: Fri, 8 Jan 2021 20:49:33 +0100 From: Peter Zijlstra To: Vincent Guittot Cc: Mel Gorman , "Li, Aubrey" , linux-kernel , Ingo Molnar , Juri Lelli , Valentin Schneider , Qais Yousef , Dietmar Eggemann , Steven Rostedt , Ben Segall , Tim Chen , Jiang Biao Subject: Re: [RFC][PATCH 1/5] sched/fair: Fix select_idle_cpu()s cost accounting Message-ID: References: <20201214164822.402812729@infradead.org> <20201214170017.877557652@infradead.org> <20201215075911.GA3040@hirez.programming.kicks-ass.net> <20210108102738.GB3592@techsingularity.net> <20210108144058.GD3592@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 08, 2021 at 04:10:51PM +0100, Vincent Guittot wrote: > Another thing that worries me, is that we use the avg_idle of the > local cpu, which is obviously not idle otherwise it would have been > selected, to decide how much time we should spend on looking for > another idle CPU. I'm not sure that's the right metrics to use > especially with a possibly stalled value. The thinking was that if this CPU has little idle time, this CPU should not spend a lot of time searching... That is; if we spend more time looking for places to run, than we have idle time, we're loosing cycles we could've ran (supposedly useful) work. The only counter argument is tail latency.