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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 BBE1BC2BB85 for ; Fri, 10 Apr 2020 03:56:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 94A5D2063A for ; Fri, 10 Apr 2020 03:56:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586490992; bh=0Lo7CKmDANSyxdZ2yOhcCNB85j0IE61I8BCTf6STT7M=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=m+LqQvDS+PGQCLtLRyBsrOmPxdWbWGkQ1UgcF+hYP3hrG0tYAR7v3/PS2vcGi9JnL NJK7BOHV3hQvNBuM1EjAvY+lz1YYkdrUIU4tLM2odBliCBjqrU+cfMaG/SWIPF7zmH ThK8BhtlIYncGPJ7guOIB0XmAoYn/5NSF6T+usb4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728603AbgDJDtk (ORCPT ); Thu, 9 Apr 2020 23:49:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:33622 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728564AbgDJDtd (ORCPT ); Thu, 9 Apr 2020 23:49:33 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 333CA20A8B; Fri, 10 Apr 2020 03:49:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586490572; bh=0Lo7CKmDANSyxdZ2yOhcCNB85j0IE61I8BCTf6STT7M=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GcaBRntt7nFJxG8ZbKrjtAXb1araSu/i3GwLNk7ppkJMeX/CtqNssGOl8LcIV2EeT eyKMqYxgoffnIBGg7jrdWK62XKLP6CYt7KdHnUvludboy0ZbfMMMpA+wGaDbTzl33U 8nXyzkXmIXNtcPFfZjH1KMK+bsSLl6QiWa3KNra4= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Michael Wang , Peter Zijlstra , Vincent Guittot , Sasha Levin Subject: [PATCH AUTOSEL 5.4 19/46] sched: Avoid scale real weight down to zero Date: Thu, 9 Apr 2020 23:48:42 -0400 Message-Id: <20200410034909.8922-19-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200410034909.8922-1-sashal@kernel.org> References: <20200410034909.8922-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore 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 e5e2605778c97..c7e7481968bfa 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