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 BBA5AC4361B for ; Mon, 14 Dec 2020 09:33:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 68F6E207B2 for ; Mon, 14 Dec 2020 09:33:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391090AbgLNJdV (ORCPT ); Mon, 14 Dec 2020 04:33:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55828 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726876AbgLNJc7 (ORCPT ); Mon, 14 Dec 2020 04:32:59 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8A73CC0613D3 for ; Mon, 14 Dec 2020 01:32:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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=YUoipkrrpYhnigWXpgpKxtM4aoanwWNczHgeVzWov4I=; b=HZPzONIdrjODcOlP/tE5pkCK+D UzcL1hrOa9yeBRpou0ey8eMYH2AfpNVHgk50HNm3VyM++4M2zYPtaSW0B3DdEC2kmzNGDyT16+cgM 8ViyrOpZNnJY8WHvgcP9LSTGeWwD7u0Mm30NDgJRB908oJh2FAjdNTf+rxaFNID3crCiPzRi37L0/ KGv6ctfhLYucXLd33gwcYrHlzfRO10Ri4k2LDwqUXPKvoVftD+RCoW8KgOxmIGtvcuhM77lPhxbUL YuyzTGQGcqoI65W1CUVZJjLhEJ1KSxTXeC9FH7bvQpPG4hMo5cWmWAX1PsEbf2HFNdSZFOUe6WjzL okq87/ag==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kokDA-0005i3-IN; Mon, 14 Dec 2020 09:32:08 +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 E5C7D3059C6; Mon, 14 Dec 2020 10:32:07 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D74802BA1531B; Mon, 14 Dec 2020 10:32:07 +0100 (CET) Date: Mon, 14 Dec 2020 10:32:07 +0100 From: Peter Zijlstra To: Mel Gorman Cc: "Li, Aubrey" , mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, valentin.schneider@arm.com, qais.yousef@arm.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, tim.c.chen@linux.intel.com, linux-kernel@vger.kernel.org, Mel Gorman , Jiang Biao Subject: Re: [RFC PATCH v7] sched/fair: select idle cpu from idle cpumask for task wakeup Message-ID: <20201214093207.GY3040@hirez.programming.kicks-ass.net> References: <20201209062404.175565-1-aubrey.li@linux.intel.com> <20201209143510.GO3371@techsingularity.net> <3802e27a-56ed-9495-21b9-7c4277065155@linux.intel.com> <20201210113441.GS3371@techsingularity.net> <31308700-aa28-b1f7-398e-ee76772b6b87@linux.intel.com> <20201210125833.GT3371@techsingularity.net> <20201211174442.GU3040@hirez.programming.kicks-ass.net> <20201211204337.GX3371@techsingularity.net> <20201211221905.GV3040@hirez.programming.kicks-ass.net> <20201211225002.GY3371@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201211225002.GY3371@techsingularity.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 11, 2020 at 10:50:02PM +0000, Mel Gorman wrote: > > > The third potential downside is that the SMT sibling is not guaranteed to > > > be checked due to SIS_PROP throttling but in the old code, that would have > > > been checked by select_idle_smt(). That might result in premature stacking > > > of runnable tasks on the same CPU. Similarly, as __select_idle_core may > > > find multiple idle candidates, it will not pick the targets SMT sibling > > > if it is idle like select_idle_smt would have. > > > > > > That said, I am skeptical that select_idle_smt() matters all that often. > > > > This, I didn't really believe in it either. > > > > Good because I think any benefit from select_idle_smt is so marginal > that it should be ignored if the full scan is simpler overall. Perhaps we should start out with a simple patch removing that pass.. That should show, what, if anything, the effect of it is.