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:   Thu, 7 Jun 2018 13:19:26 +0200
From:   Jakub Raček <jracek@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
        Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org
Subject: Re: [4.17 regression] Performance drop on kernel-4.17 visible on
 Stream, Linpack and NAS parallel benchmarks

Hi,

On 06/07/2018 01:07 PM, Michal Hocko wrote:
> [CCing Mel and MM mailing list]
> 
> On Wed 06-06-18 14:27:32, Jakub Racek 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.
> 
> Do you have numa balancing enabled?
> 

Yes. The relevant settings are:

kernel.numa_balancing = 1
kernel.numa_balancing_scan_delay_ms = 1000
kernel.numa_balancing_scan_period_max_ms = 60000
kernel.numa_balancing_scan_period_min_ms = 1000
kernel.numa_balancing_scan_size_mb = 256


-- 
Best regards,
Jakub Racek
FMK