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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 914AAC0032E for ; Sat, 28 Oct 2023 06:38:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229481AbjJ1GiH (ORCPT ); Sat, 28 Oct 2023 02:38:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45344 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229458AbjJ1GiF (ORCPT ); Sat, 28 Oct 2023 02:38:05 -0400 Received: from mail3-relais-sop.national.inria.fr (mail3-relais-sop.national.inria.fr [192.134.164.104]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7337D11B for ; Fri, 27 Oct 2023 23:38:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=inria.fr; s=dc; h=date:from:to:cc:subject:in-reply-to:message-id: references:mime-version; bh=TpjAkzYedyZU8caQY65fA7BKsB1dxSgkhWgaBHUI8JU=; b=eSIqmUdiE9luoQvnw/3CL/qaK/0Kn1awq21BUZGf27qojhMKI32laT4a sHq2qas1dSln2fVGzNTv/nI9KZudqDGoNmSOkxlzh7cgTniGAkgdaeFfF XQsZB40asKgx8XCsgnB9VEZeZMBu8QYuQZD6ScPt1jSoa5dFi3iPGka6A Q=; Authentication-Results: mail3-relais-sop.national.inria.fr; dkim=none (message not signed) header.i=none; spf=SoftFail smtp.mailfrom=julia.lawall@inria.fr; dmarc=fail (p=none dis=none) d=inria.fr X-IronPort-AV: E=Sophos;i="6.03,258,1694728800"; d="scan'208";a="70000203" Received: from 231.85.89.92.rev.sfr.net (HELO hadrien) ([92.89.85.231]) by mail3-relais-sop.national.inria.fr with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Oct 2023 08:38:00 +0200 Date: Sat, 28 Oct 2023 08:37:59 +0200 (CEST) From: Julia Lawall X-X-Sender: jll@hadrien To: Chen Yu cc: Keisuke Nishimura , Ingo Molnar , Peter Zijlstra , Vincent Guittot , linux-kernel@vger.kernel.org, Dietmar Eggemann , Mel Gorman , Valentin Schneider , Julia Lawall , Ricardo Neri , Tim Chen Subject: Re: [PATCH] sched/fair: Fix the decision for load balance In-Reply-To: Message-ID: References: <20231027171742.1426070-1-keisuke.nishimura@inria.fr> User-Agent: Alpine 2.22 (DEB 394 2020-01-19) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 28 Oct 2023, Chen Yu wrote: > On 2023-10-27 at 19:17:43 +0200, Keisuke Nishimura wrote: > > should_we_balance is called for the decision to do load-balancing. > > When sched ticks invoke this function, only one CPU should return > > true. However, in the current code, two CPUs can return true. The > > following situation, where b means busy and i means idle, is an > > example because CPU 0 and CPU 2 return true. > > > > [0, 1] [2, 3] > > b b i b > > > > This fix checks if there exists an idle CPU with busy sibling(s) > > after looking for a CPU on an idle core. If some idle CPUs with busy > > siblings are found, just the first one should do load-balancing. > > > > Fixes: b1bfeab9b002 ("sched/fair: Consider the idle state of the whole core for load balance") > > Signed-off-by: Keisuke Nishimura > > --- > > kernel/sched/fair.c | 5 +++-- > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 2048138ce54b..eff0316d6c7d 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -11083,8 +11083,9 @@ static int should_we_balance(struct lb_env *env) > > return cpu == env->dst_cpu; > > } > > > > - if (idle_smt == env->dst_cpu) > > - return true; > > + /* Is there an idle CPU with busy siblings? */ > > + if (idle_smt != -1) > > + return idle_smt == env->dst_cpu; > > > > /* Are we the first CPU of this group ? */ > > return group_balance_cpu(sg) == env->dst_cpu; > > Looks reasonable to me, if there is other idle SMT(from half-busy core) > in the system, we should leverage that SMT to do the periodic lb. > Per my understanding, That's not the goal of this patch. The goal of this patch is to avoid doing return group_balance_cpu(sg) == env->dst_cpu; when a half-busy core has been identified that is different from env->dst_cpu. julia > > Reviewed-by: Chen Yu > > thanks, > Chenyu >