linux-kernel - Re: [PATCH 5.10+5.4 0/3] sched/topology: Fix missing scheduling domain levels

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Message-ID: <YiO/EsBd0QlDA9o4@kroah.com>
Date:   Sat, 5 Mar 2022 20:50:42 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     dann frazier <dann.frazier@...onical.com>
Cc:     stable@...r.kernel.org, Miao Xie <miaox@...fujitsu.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Barry Song <song.bao.hua@...ilicon.com>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Sergei Trofimovich <slyfox@...too.org>,
        Anatoly Pugachev <matorola@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5.10+5.4 0/3] sched/topology: Fix missing scheduling
 domain levels

On Sat, Mar 05, 2022 at 09:44:27AM -0700, dann frazier wrote:
> The LTP cpuset_sched_domains test, authored by Miao Xie, fails on a Kunpeng920
> server that has 4 NUMA nodes:
>   https://launchpad.net/bugs/1951289
> 
> This does appear to be a real bug. /proc/schedstat displays 4 domain levels for
> CPUs on 2 of the nodes, but only 3 levels for the others 2 (see below).
> I assume this means the scheduler is making suboptimal decisions about
> where to place/move processes. I'm not sure how to demonstrate that - but
> open to suggestions if that evidence is important justification for stable.
> 
> This is not a problem in current upstream kernels, so I bisected and found
> that the first patch here fixes it. I can't tell from the commit message
> if fixing this case was Valentin's intent, or just a happy side-effect of the
> set conversion. The other two patches fix regressions introduced by the first.
> All cherry-pick cleanly back to 5.10.y and 5.4.y. This platform easily
> reproduces the problem Dietmar's fix addresses. I don't have hardware to test
> the ia64 fix.
> 
> Note: This also impacts earlier stable trees, but require some minor porting,
> so I'll submit fixes for those separately.
> 
> Here's a comparison of /proc/schedstat before & after applying these
> fixes:

Thanks, now queued up.

greg k-h