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,URIBL_BLOCKED,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 F405CC352BE for ; Thu, 16 Apr 2020 15:29:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CFEBE214AF for ; Thu, 16 Apr 2020 15:29:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587050971; bh=JuRk7IwZErEkQs154JWgYaEIehaHU2r9Jj03bNGW2qc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=nh7lcWwrJPjeWgPsg8FAa5X4QFsp2RxhbDWs2kEeweQcD0EBOWzmvYARI0TLdpL6P /EvW8ZKdHL8S/Rmi13sedXGuNHr0sgITMKI8EnhdXX3A8pfy96O6Mb+jTVx3WDLZjW OyYnnVUw8aJuNyBZosiypmjJnv/fYII4fwZ+o3zI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2898016AbgDPNnw (ORCPT ); Thu, 16 Apr 2020 09:43:52 -0400 Received: from mail.kernel.org ([198.145.29.99]:45184 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2896794AbgDPNdu (ORCPT ); Thu, 16 Apr 2020 09:33:50 -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 A80D0221EB; Thu, 16 Apr 2020 13:33:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587044030; bh=JuRk7IwZErEkQs154JWgYaEIehaHU2r9Jj03bNGW2qc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mpKTnkXArQkIV8Fvy+cvXyTvNEl5eVSRZjfgZ+YU64ykIXslgEfje9GJdybz0DgPh jPah3rX6BK/OF18Di/isO19vEZWRVdUsk4sRLMDasL5Fv/jWOG1b60l6WC5m0lB/69 DWoiZDePI7kCpjpikxRUWAYy7sf04IqWghYY/P+4= 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 5.5 052/257] sched: Avoid scale real weight down to zero Date: Thu, 16 Apr 2020 15:21:43 +0200 Message-Id: <20200416131332.452089698@linuxfoundation.org> X-Mailer: git-send-email 2.26.1 In-Reply-To: <20200416131325.891903893@linuxfoundation.org> References: <20200416131325.891903893@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 280a3c7359355..0502ea8e0e62a 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -118,7 +118,13 @@ extern long calc_load_fold_active(struct rq *this_rq, long adjust); #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