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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 9CCFEC433FE for ; Fri, 4 Dec 2020 15:41:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 58E0622B30 for ; Fri, 4 Dec 2020 15:41:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729454AbgLDPlX (ORCPT ); Fri, 4 Dec 2020 10:41:23 -0500 Received: from outbound-smtp31.blacknight.com ([81.17.249.62]:44885 "EHLO outbound-smtp31.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727125AbgLDPlX (ORCPT ); Fri, 4 Dec 2020 10:41:23 -0500 Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp31.blacknight.com (Postfix) with ESMTPS id 05DF8C0DFA for ; Fri, 4 Dec 2020 15:40:31 +0000 (GMT) Received: (qmail 5873 invoked from network); 4 Dec 2020 15:40:30 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 4 Dec 2020 15:40:30 -0000 Date: Fri, 4 Dec 2020 15:40:29 +0000 From: Mel Gorman To: Vincent Guittot Cc: "Li, Aubrey" , LKML , Barry Song , Ingo Molnar , Peter Ziljstra , Juri Lelli , Valentin Schneider , Linux-ARM Subject: Re: [PATCH 06/10] sched/fair: Clear the target CPU from the cpumask of CPUs searched Message-ID: <20201204154029.GC3371@techsingularity.net> References: <20201203175204.GY3371@techsingularity.net> <20201204113030.GZ3371@techsingularity.net> <3d8a6d19-afac-dc93-127d-da6505402cdf@linux.intel.com> <20201204143115.GB3371@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 04, 2020 at 04:23:48PM +0100, Vincent Guittot wrote: > On Fri, 4 Dec 2020 at 15:31, Mel Gorman wrote: > > > > On Fri, Dec 04, 2020 at 02:47:48PM +0100, Vincent Guittot wrote: > > > > IIUC, select_idle_core and select_idle_cpu share the same cpumask(select_idle_mask)? > > > > If the target's sibling is removed from select_idle_mask from select_idle_core(), > > > > select_idle_cpu() will lose the chance to pick it up? > > > > > > This is only relevant for patch 10 which is not to be included IIUC > > > what mel said in cover letter : "Patches 9 and 10 are stupid in the > > > context of this series." > > > > > > > Patch 10 was stupid in the context of the prototype because > > select_idle_core always returned a CPU. A variation ended up being > > reintroduced at the end of the Series Yet To Be Posted so that SMT siblings > > are cleared during select_idle_core() but select_idle_cpu() still has a > > mask with unvisited CPUs to consider if no idle cores are found. > > > > As far as I know, this would still be compatible with Aubrey's idle > > cpu mask as long as it's visited and cleared between select_idle_core > > and select_idle_cpu. It relaxes the contraints on Aubrey to some extent > > because the idle cpu mask would be a hint so if the information is out > > of date, an idle cpu may still be found the normal way. > > But even without patch 10, just replacing sched_domain_span(sd) by > sds_idle_cpus(sd->shared) will ensure that sis loops only on cpus that > get a chance to be idle so select_idle_core is likely to return an > idle_candidate > Yes but if the idle mask is out of date for any reason then idle CPUs might be missed -- hence the intent to maintain a mask of CPUs visited and use the idle cpu mask as a hint to prioritise CPUs that are likely idle but fall back to a normal scan if none of the "idle cpu mask" CPUs are actually idle. -- Mel Gorman SUSE Labs