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=-14.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=ham 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 857B0C432C0 for ; Tue, 3 Dec 2019 23:31:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 530892068E for ; Tue, 3 Dec 2019 23:31:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="VVd+jIIq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726395AbfLCXbI (ORCPT ); Tue, 3 Dec 2019 18:31:08 -0500 Received: from mail-wm1-f66.google.com ([209.85.128.66]:51823 "EHLO mail-wm1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726144AbfLCXbH (ORCPT ); Tue, 3 Dec 2019 18:31:07 -0500 Received: by mail-wm1-f66.google.com with SMTP id g206so5074808wme.1 for ; Tue, 03 Dec 2019 15:31:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Y8UcjpPXP0dkBwA69LJ0NpHT+UcdWSS4UtsNwrG9naw=; b=VVd+jIIqv/fZbl8HJH6MpkCVFVQ3wFQ8llBTT/wLdAAkbl8eW1yviv8q3DGYSciqUA sqa8gNx98no8UWiyhpQoojgqAfHfhgzvdCWF8IAD5vd689Ls+j7wl1Ky3dODMONQ8uwA bT7OCzDfYWUz1HG5ATYy2nNNLgiLeO5GIIOrSo/WqFVTTRmYGAttRnVp5rP4MFvyl6Cd wF8rufwLmVXWBMIHqZK7mk15Ev4ocuuSVP40yBkpnghB02WVnbnmImx3GBhNqCMJtKtF noYLJj9QR07uCJ2lVtSiD1KXjpVb63CKzVVrDr9nuh8tOFiJzfbNzKk+Z4uUk5PW3fYl W/5w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Y8UcjpPXP0dkBwA69LJ0NpHT+UcdWSS4UtsNwrG9naw=; b=JNH3+iMtftTwHV1RIQCyWaz+yuCvvnQY54rP19/+3pFZ6c6ZSZJZBCnr4tz573dTB2 qqdUlwvc7NLtGdtP4uUil1KhbsYvAzc5bjm2CaHlaa0Y1+gs1HNoDPfWhiqzveusk/ot 7i/QWblDfYrfoBhQ4eZRKX1GHhXOthFP4UPYOOWjBzWyzFQg26D9C/0PP0caQuynXp/m H6QktS2+mQDCq7YrYzfVakxUutrwbcdZZ+cY5VSdRMkt3scwHELxXLH1TxGOvzNmJpH1 bBmBYcNZOnWVaJCG+ir1rsJytzRWfbOTXcY9AJkeQ9vaci2JC9uaGb6yS09WOwCI0iDw KTgQ== X-Gm-Message-State: APjAAAUz5Wh9e9LpMUESUfo1wddWxfssKIQc9yzyxCHNncq2P2dK3FAM SZ58qUwmZC9G9KFtoUc+r9tgKFW0QZu4ClRXWB5mpg== X-Google-Smtp-Source: APXvYqyGpAnPog5jh2rVlqBoxDi0Lr8PEA/g6DfdhwatQXkXFEzLOPSBSG9StDKYdaOCgZsXA7+XwrDGP69IuUohkJs= X-Received: by 2002:a7b:cd83:: with SMTP id y3mr39136133wmj.168.1575415864420; Tue, 03 Dec 2019 15:31:04 -0800 (PST) MIME-Version: 1.0 References: <20191203230944.GA3495297@kroah.com> In-Reply-To: From: Xuewei Zhang Date: Tue, 3 Dec 2019 15:30:52 -0800 Message-ID: Subject: Re: Request to backport 4929a4e6faa0 to stable tree To: Greg KH Cc: stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org Backport patch that cleanly applies for 4.19, 4.14, 4.9, 4.4 stable trees: >From 199df9edf62c339b5459fc53d4631c82a3b82f5b Mon Sep 17 00:00:00 2001 From: Xuewei Zhang Date: Thu, 3 Oct 2019 17:12:43 -0700 Subject: [PATCH] sched/fair: Scale bandwidth quota and period without losing quota/period ratio precision 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. Change-Id: I3d5f7629012ff115557a08c465a95a5239a105de 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 Cc: Xuewei Zhang --- kernel/sched/fair.c | 36 ++++++++++++++++++++++-------------- 1 file changed, 22 insertions(+), 14 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index ea2d33aa1f55..773135f534ef 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3753,20 +3753,28 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer) if (++count > 3) { u64 new, old = ktime_to_ns(cfs_b->period); - new = (old * 147) / 128; /* ~115% */ - new = min(new, max_cfs_quota_period); - - 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)); + /* + * 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; + + 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; -- 2.24.0.393.g34dc348eaf-goog