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=-10.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,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 27B24C433DF for ; Mon, 10 Aug 2020 08:55:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0277620678 for ; Mon, 10 Aug 2020 08:55:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726547AbgHJIzj (ORCPT ); Mon, 10 Aug 2020 04:55:39 -0400 Received: from foss.arm.com ([217.140.110.172]:54270 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725857AbgHJIzi (ORCPT ); Mon, 10 Aug 2020 04:55:38 -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 0313A11B3; Mon, 10 Aug 2020 01:55:38 -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 882EA3F7BB; Mon, 10 Aug 2020 01:55:36 -0700 (PDT) References: <20200804105619.GE2657@hirez.programming.kicks-ass.net> <20200804193413.510651-1-joshdon@google.com> <20200810061406.GA15559@linux.vnet.ibm.com> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Srikar Dronamraju Cc: Josh Don , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] sched/fair: ignore cache hotness for SMT migration In-reply-to: <20200810061406.GA15559@linux.vnet.ibm.com> Date: Mon, 10 Aug 2020 09:55:31 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/08/20 07:14, Srikar Dronamraju wrote: > * Josh Don [2020-08-04 12:34:13]: > >> SMT siblings share caches, so cache hotness should be irrelevant for >> cross-sibling migration. >> >> Proposed-by: Venkatesh Pallipadi >> Signed-off-by: Josh Don >> --- >> kernel/sched/fair.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 1a68a0536add..abdb54e2339f 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -7402,6 +7402,10 @@ static int task_hot(struct task_struct *p, struct lb_env *env) >> if (unlikely(task_has_idle_policy(p))) >> return 0; >> >> + /* SMT siblings share cache */ >> + if (env->sd->flags & SD_SHARE_CPUCAPACITY) >> + return 0; >> + > > If this for retaining cache hotness, should we look at > SD_SHARE_PKG_RESOURCES instead of SD_SHARE_CPUCAPACITY? > Josh's patch only targets migrating tasks between threads of the same core - as he points out, cache hotness shouldn't matter here. Using SD_SHARE_PKG_RESOURCES here would mean freely migrating tasks between any CPU of an LLC domain, which is quite likely something you do *not* want to do. >> /* >> * Buddy candidates are cache hot: >> */ >> -- >> 2.28.0.163.g6104cc2f0b6-goog >>