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SubjectRe: [PATCH 2/6] mm/migrate: Use trylock while resetting rate limit

* Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote:

> Since this spinlock will only serialize migrate rate limiting,
> convert the spinlock to a trylock. If another task races ahead of this task
> then this task can simply move on.
>
> While here, add correct two abnormalities.
> - Avoid time being stretched for every interval.
> - Use READ/WRITE_ONCE with next window.
>
> specjbb2005 / bops/JVM / higher bops are better
> on 2 Socket/2 Node Intel
> JVMS Prev Current %Change
> 4 206350 200892 -2.64502
> 1 319963 325766 1.81365
>
>
> on 2 Socket/2 Node Power9 (PowerNV)
> JVMS Prev Current %Change
> 4 186539 190261 1.99529
> 1 220344 195305 -11.3636
>
>
> on 4 Socket/4 Node Power7
> JVMS Prev Current %Change
> 8 56836 57651.1 1.43413
> 1 112970 111351 -1.43312
>
>
> dbench / transactions / higher numbers are better
> on 2 Socket/2 Node Intel
> count Min Max Avg Variance %Change
> 5 13136.1 13170.2 13150.2 14.7482
> 5 12254.7 12331.9 12297.8 28.1846 -6.48203
>
>
> on 2 Socket/4 Node Power8 (PowerNV)
> count Min Max Avg Variance %Change
> 5 4319.79 4998.19 4836.53 261.109
> 5 4997.83 5030.14 5015.54 12.947 3.70121
>
>
> on 2 Socket/2 Node Power9 (PowerNV)
> count Min Max Avg Variance %Change
> 5 9325.56 9402.7 9362.49 25.9638
> 5 9331.84 9375.11 9352.04 16.0703 -0.111616
>
>
> on 4 Socket/4 Node Power7
> count Min Max Avg Variance %Change
> 5 132.581 191.072 170.554 21.6444
> 5 147.55 181.605 168.963 11.3513 -0.932842

Firstly, *please* always characterize benchmark runs. What did you find? How should we
interpret the result? Are there any tradeoffs?

*Don't* just dump them on us.

Because in this particular case the results are not obvious, at all:

> specjbb2005 / bops/JVM / higher bops are better
> on 2 Socket/2 Node Intel
> JVMS Prev Current %Change
> 4 206350 200892 -2.64502
> 1 319963 325766 1.81365
>
>
> on 2 Socket/2 Node Power9 (PowerNV)
> JVMS Prev Current %Change
> 4 186539 190261 1.99529
> 1 220344 195305 -11.3636
>
>
> on 4 Socket/4 Node Power7
> JVMS Prev Current %Change
> 8 56836 57651.1 1.43413
> 1 112970 111351 -1.43312

Why is this better? The largest drop is 11% which seems significant.

Thanks,

Ingo

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