linux-kernel - Re: [4.17 regression] Performance drop on kernel-4.17 visible on Stream, Linpack and NAS parallel benchmarks

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Date:   Wed, 6 Jun 2018 14:34:32 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Jakub Racek <jracek@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [4.17 regression] Performance drop on kernel-4.17 visible on
 Stream, Linpack and NAS parallel benchmarks

On Wed, Jun 6, 2018 at 2:27 PM, Jakub Racek <jracek@...hat.com> wrote:
> Hi,
>
> There is a huge performance regression on the 2 and 4 NUMA node systems on
> stream benchmark with 4.17 kernel compared to 4.16 kernel. Stream, Linpack
> and NAS parallel benchmarks show upto 50% performance drop.
>
> When running for example 20 stream processes in parallel, we see the
> following behavior:
>
> * all processes are started at NODE #1
> * memory is also allocated on NODE #1
> * roughly half of the processes are moved to the NODE #0 very quickly. *
> however, memory is not moved to NODE #0 and stays allocated on NODE #1
>
> As the result, half of the processes are running on NODE#0 with memory being
> still allocated on NODE#1. This leads to non-local memory accesses
> on the high Remote-To-Local Memory Access Ratio on the numatop charts.
> So it seems that 4.17 is not doing a good job to move the memory to the
> right NUMA
> node after the process has been moved.
>
> ----8<----
>
> The above is an excerpt from performance testing on 4.16 and 4.17 kernels.
>
> For now I'm merely making sure the problem is reported.

OK, and why do you think that it is related to ACPI?

Thanks,
Rafael