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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 1AAD8C43603 for ; Wed, 11 Dec 2019 15:25:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E4FA722B48 for ; Wed, 11 Dec 2019 15:25:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576077959; bh=IHw4jTrj90jwghLdygQZLnHQsF6pcR9FAhOyEfCP6es=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=eXbRZE21wxdnHVTN16PFeZD109uwDVfZlfe75QKDFg8R5qA4nGbKxzoDuPQJEcLX/ 2IUMNSjkkG16f/qG7tZjhy8NRJZvCbZh4tCtgpIlyu3wARoI5go3RizJBKsDLJG+fH EZ2o9gHZcny50NY1S0CzG5DNvv6fJccRgdcVpklQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730584AbfLKPZ6 (ORCPT ); Wed, 11 Dec 2019 10:25:58 -0500 Received: from mail.kernel.org ([198.145.29.99]:58524 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732885AbfLKPZx (ORCPT ); Wed, 11 Dec 2019 10:25:53 -0500 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 E9EE7208C3; Wed, 11 Dec 2019 15:25:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576077952; bh=IHw4jTrj90jwghLdygQZLnHQsF6pcR9FAhOyEfCP6es=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZC1sdaS2zNqaMlkJGEyqp3D+pBpmgdYpNC0ivgZYt5E5I7yeoFQmRamGVvx0QAB56 Xd2SIEUKtTvcB9gmohSDjfHyF0s6LXqgYChVA9sr4fKTclutqEIBUqCbiMFH4JxilG 3vXMO0MncN0AB/oSBkPHZBCfpY79l2QG2PFqedys= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Phil Auld , Xuewei Zhang , "Peter Zijlstra (Intel)" , Anton Blanchard , Ben Segall , Dietmar Eggemann , Juri Lelli , Linus Torvalds , Mel Gorman , Steven Rostedt , Thomas Gleixner , Vincent Guittot , Ingo Molnar Subject: [PATCH 4.19 196/243] sched/fair: Scale bandwidth quota and period without losing quota/period ratio precision Date: Wed, 11 Dec 2019 16:05:58 +0100 Message-Id: <20191211150352.410946163@linuxfoundation.org> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20191211150339.185439726@linuxfoundation.org> References: <20191211150339.185439726@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: Xuewei Zhang commit 4929a4e6faa0f13289a67cae98139e727f0d4a97 upstream. The quota/period ratio is used to ensure a child task group won't get more bandwidth than the parent task group, and is calculated as: normalized_cfs_quota() = [(quota_us << 20) / period_us] If the quota/period ratio was changed during this scaling due to precision loss, it will cause inconsistency between parent and child task groups. See below example: A userspace container manager (kubelet) does three operations: 1) Create a parent cgroup, set quota to 1,000us and period to 10,000us. 2) Create a few children cgroups. 3) Set quota to 1,000us and period to 10,000us on a child cgroup. These operations are expected to succeed. However, if the scaling of 147/128 happens before step 3, quota and period of the parent cgroup will be changed: new_quota: 1148437ns, 1148us new_period: 11484375ns, 11484us And when step 3 comes in, the ratio of the child cgroup will be 104857, which will be larger than the parent cgroup ratio (104821), and will fail. Scaling them by a factor of 2 will fix the problem. Tested-by: Phil Auld Signed-off-by: Xuewei Zhang Signed-off-by: Peter Zijlstra (Intel) Acked-by: Phil Auld Cc: Anton Blanchard Cc: Ben Segall Cc: Dietmar Eggemann Cc: Juri Lelli Cc: Linus Torvalds Cc: Mel Gorman Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Vincent Guittot Fixes: 2e8e19226398 ("sched/fair: Limit sched_cfs_period_timer() loop to avoid hard lockup") Link: https://lkml.kernel.org/r/20191004001243.140897-1-xueweiz@google.com Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- kernel/sched/fair.c | 34 +++++++++++++++++++++------------- 1 file changed, 21 insertions(+), 13 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4868,20 +4868,28 @@ static enum hrtimer_restart sched_cfs_pe if (++count > 3) { u64 new, old = ktime_to_ns(cfs_b->period); - new = (old * 147) / 128; /* ~115% */ - new = min(new, max_cfs_quota_period); + /* + * Grow period by a factor of 2 to avoid losing precision. + * Precision loss in the quota/period ratio can cause __cfs_schedulable + * to fail. + */ + new = old * 2; + if (new < max_cfs_quota_period) { + cfs_b->period = ns_to_ktime(new); + cfs_b->quota *= 2; - cfs_b->period = ns_to_ktime(new); - - /* since max is 1s, this is limited to 1e9^2, which fits in u64 */ - cfs_b->quota *= new; - cfs_b->quota = div64_u64(cfs_b->quota, old); - - pr_warn_ratelimited( - "cfs_period_timer[cpu%d]: period too short, scaling up (new cfs_period_us %lld, cfs_quota_us = %lld)\n", - smp_processor_id(), - div_u64(new, NSEC_PER_USEC), - div_u64(cfs_b->quota, NSEC_PER_USEC)); + pr_warn_ratelimited( + "cfs_period_timer[cpu%d]: period too short, scaling up (new cfs_period_us = %lld, cfs_quota_us = %lld)\n", + smp_processor_id(), + div_u64(new, NSEC_PER_USEC), + div_u64(cfs_b->quota, NSEC_PER_USEC)); + } else { + pr_warn_ratelimited( + "cfs_period_timer[cpu%d]: period too short, but cannot scale up without losing precision (cfs_period_us = %lld, cfs_quota_us = %lld)\n", + smp_processor_id(), + div_u64(old, NSEC_PER_USEC), + div_u64(cfs_b->quota, NSEC_PER_USEC)); + } /* reset count so we don't come right back in here */ count = 0;