From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:36952 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727294AbeJSBC5 (ORCPT ); Thu, 18 Oct 2018 21:02:57 -0400 Date: Thu, 18 Oct 2018 19:01:02 +0200 From: Greg Kroah-Hartman To: Ivan Delalande Cc: Frederic Weisbecker , Ingo Molnar , Rabin Vincent , Edward Chron , stable@vger.kernel.org Subject: Re: [PATCH 4.9 v2 0/4] Fix softirq time accounting issues on 4.9 Message-ID: <20181018170102.GF11159@kroah.com> References: <20181013021059.4764-1-colona@arista.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181013021059.4764-1-colona@arista.com> Sender: stable-owner@vger.kernel.org List-ID: On Fri, Oct 12, 2018 at 07:10:55PM -0700, Ivan Delalande wrote: > Hi Greg, > > This series fixes issues we've seen with softirq time accounting in 4.9: > - when ksoftirqd is running at 100% on a CPU, none of the values > reported by /proc/stat for that CPU will change, sometimes for > dozens of seconds, > - large deviations in the total number of ticks accumulated over a > fixed time for a CPU, probably because of the first issue hitting > for shorter periods. > > We found out that something pretty similar had been reported 9 months > ago, see the reference link below. In that discussion, Rabin Vincent had > made a 4.9 specific patch which fixes our first issue, but we were still > seeing some deviation from the total number of ticks (up to 1.7% from > expected, where we had only 0.2% on older kernels), and you had also > asked for a direct backport from the mainline series, if possible. > > As mentioned in that thread, a lot of changes (probably 50+) went into > 4.11 to remove cputime, but we could get something working with only the > 4 attached patches to fix these two issues. Three of these patches apply > without change, and the second one in the series ("sched/cputime: > Convert kcpustat to nsecs") needed a minor change as a cast had been > added in 527b0a76f41d ("sched/cpuacct: Avoid %lld seq_printf warning") > to fix a build warning on s390. I guess we could also include that patch > in this series, let me know if this is the preferred way to handle this. > > We ran our tests on 3.18, 4.4 and 4.9 and confirmed that only 4.9 would > need this series, and that this series indeed restores the behavior we > were seeing on those older kernels. > > Thanks! > > Reference: http://lkml.kernel.org/r/%3C1513159876-5125-1-git-send-email-rabin.vincent@axis.com > > > v2: - drop "time: Introduce jiffies64_to_nsecs()" as it has already been > merged into v4.9.132, > - include backport of commit 564b733c899f ("macintosh/rack-meter: > Convert cputime64_t use to u64") to avoid introducing a build > failure on powerpc. Ok, let's try this again, all queued up. greg k-h