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=-13.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 9F9FCC10F0E for ; Tue, 9 Apr 2019 12:48:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6DEB720855 for ; Tue, 9 Apr 2019 12:48:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727104AbfDIMsU (ORCPT ); Tue, 9 Apr 2019 08:48:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54516 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726486AbfDIMsT (ORCPT ); Tue, 9 Apr 2019 08:48:19 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E8E143001C86; Tue, 9 Apr 2019 12:48:18 +0000 (UTC) Received: from pauld.bos.csb (dhcp-17-51.bos.redhat.com [10.18.17.51]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D70416A970; Tue, 9 Apr 2019 12:48:17 +0000 (UTC) Date: Tue, 9 Apr 2019 08:48:16 -0400 From: Phil Auld To: linux-kernel@vger.kernel.org, hpa@zytor.com, peterz@infradead.org, bsegall@google.com, torvalds@linux-foundation.org, anton@ozlabs.org, efault@gmx.de, mingo@kernel.org, tglx@linutronix.de Cc: linux-tip-commits@vger.kernel.org Subject: Re: [tip:sched/core] sched/fair: Limit sched_cfs_period_timer loop to avoid hard lockup Message-ID: <20190409124815.GA10132@pauld.bos.csb> References: <20190319130005.25492-1-pauld@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Tue, 09 Apr 2019 12:48:19 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ingo, Peter, On Wed, Apr 03, 2019 at 01:38:39AM -0700 tip-bot for Phil Auld wrote: > Commit-ID: 06ec5d30e8d57b820d44df6340dcb25010d6d0fa > Gitweb: https://git.kernel.org/tip/06ec5d30e8d57b820d44df6340dcb25010d6d0fa > Author: Phil Auld > AuthorDate: Tue, 19 Mar 2019 09:00:05 -0400 > Committer: Ingo Molnar > CommitDate: Wed, 3 Apr 2019 09:50:23 +0200 This commit seems to have gotten lost. It's not in tip and now the direct gitweb link is also showing bad commit reference. Did this fall victim to a reset or something? Thanks, Phil > > sched/fair: Limit sched_cfs_period_timer loop to avoid hard lockup > > With extremely short cfs_period_us setting on a parent task group with a large > number of children the for loop in sched_cfs_period_timer can run until the > watchdog fires. There is no guarantee that the call to hrtimer_forward_now() > will ever return 0. The large number of children can make > do_sched_cfs_period_timer() take longer than the period. > > NMI watchdog: Watchdog detected hard LOCKUP on cpu 24 > RIP: 0010:tg_nop+0x0/0x10 > > walk_tg_tree_from+0x29/0xb0 > unthrottle_cfs_rq+0xe0/0x1a0 > distribute_cfs_runtime+0xd3/0xf0 > sched_cfs_period_timer+0xcb/0x160 > ? sched_cfs_slack_timer+0xd0/0xd0 > __hrtimer_run_queues+0xfb/0x270 > hrtimer_interrupt+0x122/0x270 > smp_apic_timer_interrupt+0x6a/0x140 > apic_timer_interrupt+0xf/0x20 > > > To prevent this we add protection to the loop that detects when the loop has run > too many times and scales the period and quota up, proportionally, so that the timer > can complete before then next period expires. This preserves the relative runtime > quota while preventing the hard lockup. > > A warning is issued reporting this state and the new values. > > Signed-off-by: Phil Auld > Signed-off-by: Peter Zijlstra (Intel) > Cc: Anton Blanchard > Cc: Ben Segall > Cc: Linus Torvalds > Cc: Mike Galbraith > Cc: Peter Zijlstra > Cc: Thomas Gleixner > Cc: > Link: https://lkml.kernel.org/r/20190319130005.25492-1-pauld@redhat.com > Signed-off-by: Ingo Molnar > --- > kernel/sched/fair.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 40bd1e27b1b7..d4cce633eac8 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4885,6 +4885,8 @@ static enum hrtimer_restart sched_cfs_slack_timer(struct hrtimer *timer) > return HRTIMER_NORESTART; > } > > +extern const u64 max_cfs_quota_period; > + > static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer) > { > struct cfs_bandwidth *cfs_b = > @@ -4892,6 +4894,7 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer) > unsigned long flags; > int overrun; > int idle = 0; > + int count = 0; > > raw_spin_lock_irqsave(&cfs_b->lock, flags); > for (;;) { > @@ -4899,6 +4902,28 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer) > if (!overrun) > break; > > + 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 /= 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(), > + new/NSEC_PER_USEC, > + cfs_b->quota/NSEC_PER_USEC); > + > + /* reset count so we don't come right back in here */ > + count = 0; > + } > + > idle = do_sched_cfs_period_timer(cfs_b, overrun, flags); > } > if (idle) --