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Date:   Fri, 21 Feb 2020 16:28:24 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     =?utf-8?B?546L6LSH?= <yun.wang@linux.alibaba.com>
Cc:     Mel Gorman <mgorman@suse.de>, Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>,
        Michal Koutn? <mkoutny@suse.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org,
        "Paul E. McKenney" <paulmck@linux.ibm.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Jonathan Corbet <corbet@lwn.net>
Subject: Re: [PATCH RESEND v8 1/2] sched/numa: introduce per-cgroup NUMA
 locality info
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On Mon, Feb 17, 2020 at 09:23:52PM +0800, 王贇 wrote:
> FYI, by monitoring locality, we found that the kvm vcpu thread is not
> covered by NUMA Balancing, whatever how many maximum period passed, the
> counters are not increasing, or very slowly, although inside guest we are
> copying memory.
> 
> Later we found such task rarely exit to user space to trigger task
> work callbacks, and NUMA Balancing scan depends on that, which help us
> realize the importance to enable NUMA Balancing inside guest, with the
> correct NUMA topo, a big performance risk I'll say :-P

That's a bug in KVM, see:

  https://lkml.kernel.org/r/20190801143657.785902257@linutronix.de
  https://lkml.kernel.org/r/20190801143657.887648487@linutronix.de

ISTR there being newer versions of that patch-set, but I can't seem to
find them in a hurry.