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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 4DCA1C55186 for ; Wed, 22 Apr 2020 10:03:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 28AFA20787 for ; Wed, 22 Apr 2020 10:03:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587549813; bh=nVOpzHyiyppnNvj1+1Etp1vvzi0VnZVACvXG8DhwaHo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=BeIqSqgKzZsGR513LawyBnDE/ZYbYmjVibWzynQQaDroj+CFExzDzY9fQoWCZICkb f6rht27V+j3oyzlLaEHdMvsQ1Qm8zOwMiYDgyt0Gk80vVvK1hI3pPzVJO0BE+JuO41 FaV5dxPLvrt6ha23fyRQLS7ym9eJL7WzXGvB84sw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727832AbgDVKDc (ORCPT ); Wed, 22 Apr 2020 06:03:32 -0400 Received: from mail.kernel.org ([198.145.29.99]:53160 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727813AbgDVKD0 (ORCPT ); Wed, 22 Apr 2020 06:03:26 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AE8262082E; Wed, 22 Apr 2020 10:03:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587549805; bh=nVOpzHyiyppnNvj1+1Etp1vvzi0VnZVACvXG8DhwaHo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=J96e6GnIsDNExEgXwNApYMjx/o4kje7WBTXI1RP4Ery47V78qeX584VEm9Bccf0pZ G/65B+ANcFooebmsN6bUSgq6ccMR01o7zOS63tWbM33raVCZuhxmiTfzDAw4QkA04l fnD/N/XSX7fvb0daT+6kO+1y9/LQ3d53kB+grbNg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Peter Zijlstra , Michael Wang , Vincent Guittot , Sasha Levin Subject: [PATCH 4.9 006/125] sched: Avoid scale real weight down to zero Date: Wed, 22 Apr 2020 11:55:23 +0200 Message-Id: <20200422095033.973891297@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200422095032.909124119@linuxfoundation.org> References: <20200422095032.909124119@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Michael Wang [ Upstream commit 26cf52229efc87e2effa9d788f9b33c40fb3358a ] During our testing, we found a case that shares no longer working correctly, the cgroup topology is like: /sys/fs/cgroup/cpu/A (shares=102400) /sys/fs/cgroup/cpu/A/B (shares=2) /sys/fs/cgroup/cpu/A/B/C (shares=1024) /sys/fs/cgroup/cpu/D (shares=1024) /sys/fs/cgroup/cpu/D/E (shares=1024) /sys/fs/cgroup/cpu/D/E/F (shares=1024) The same benchmark is running in group C & F, no other tasks are running, the benchmark is capable to consumed all the CPUs. We suppose the group C will win more CPU resources since it could enjoy all the shares of group A, but it's F who wins much more. The reason is because we have group B with shares as 2, since A->cfs_rq.load.weight == B->se.load.weight == B->shares/nr_cpus, so A->cfs_rq.load.weight become very small. And in calc_group_shares() we calculate shares as: load = max(scale_load_down(cfs_rq->load.weight), cfs_rq->avg.load_avg); shares = (tg_shares * load) / tg_weight; Since the 'cfs_rq->load.weight' is too small, the load become 0 after scale down, although 'tg_shares' is 102400, shares of the se which stand for group A on root cfs_rq become 2. While the se of D on root cfs_rq is far more bigger than 2, so it wins the battle. Thus when scale_load_down() scale real weight down to 0, it's no longer telling the real story, the caller will have the wrong information and the calculation will be buggy. This patch add check in scale_load_down(), so the real weight will be >= MIN_SHARES after scale, after applied the group C wins as expected. Suggested-by: Peter Zijlstra Signed-off-by: Michael Wang Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Vincent Guittot Link: https://lkml.kernel.org/r/38e8e212-59a1-64b2-b247-b6d0b52d8dc1@linux.alibaba.com Signed-off-by: Sasha Levin --- kernel/sched/sched.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 15c08752926b0..819bd5fb02647 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -73,7 +73,13 @@ static inline void update_idle_core(struct rq *rq) { } #ifdef CONFIG_64BIT # define NICE_0_LOAD_SHIFT (SCHED_FIXEDPOINT_SHIFT + SCHED_FIXEDPOINT_SHIFT) # define scale_load(w) ((w) << SCHED_FIXEDPOINT_SHIFT) -# define scale_load_down(w) ((w) >> SCHED_FIXEDPOINT_SHIFT) +# define scale_load_down(w) \ +({ \ + unsigned long __w = (w); \ + if (__w) \ + __w = max(2UL, __w >> SCHED_FIXEDPOINT_SHIFT); \ + __w; \ +}) #else # define NICE_0_LOAD_SHIFT (SCHED_FIXEDPOINT_SHIFT) # define scale_load(w) (w) -- 2.20.1