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Subject[benchmark] THP performance testcase

( Changed the subject line to make it stand out better on lkml. Mail with
link & results quoted below. )

* Alex Thorlton <athorlton@sgi.com> wrote:

> [...] Here's a pointer to the test I wrote:
>
> ftp://shell.sgi.com/collect/appsx_test/pthread_test.tar.gz
>
> Everything to compile the test should be there (just run make in the
> thp_pthread directory). To run the test use something like:
>
> time ./thp_pthread -C 0 -m 0 -c <max_cores> -b <memory>
>
> I ran:
>
> time ./thp_pthread -C 0 -m 0 -c 128 -b 128g
>
> On a 256 core machine, with ~500gb of memory and got these results:
>
> THP off:
>
> real 0m57.797s
> user 46m22.156s
> sys 6m14.220s
>
> THP on:
>
> real 1m36.906s
> user 0m2.612s
> sys 143m13.764s
>
> I snagged some code from another test we use, so I can't vouch for the
> usefulness/accuracy of all the output (actually, I know some of it is
> wrong). I've mainly been looking at the total run time.
>
> Don't want to bloat this e-mail up with too many test results, but I
> found this one really interesting. Same machine, using all the cores,
> with the same amount of memory. This means that each cpu is actually
> doing *less* work, since the chunk we reserve gets divided up evenly
> amongst the cpus:
>
> time ./thp_pthread -C 0 -m 0 -c 256 -b 128g
>
> THP off:
>
> real 1m1.028s
> user 104m58.448s
> sys 8m52.908s
>
> THP on:
>
> real 2m26.072s
> user 60m39.404s
> sys 337m10.072s
>
> Seems that the test scales really well in the THP off case, but, once
> again, with THP on, we really see the performance start to degrade.
>
> I'm planning to start investigating possible ways to split up THPs, if
> we detect that that majority of the references to a THP are off-node.
> I've heard some horror stories about migrating pages in this situation
> (i.e., process switches cpu and then all the pages follow it), but I
> think we might be able to get some better results if we can cleverly
> determine an appropriate time to split up pages. I've heard a bit of
> talk about doing something similar to this from a few people, but
> haven't seen any code/test results. If anybody has any input on that
> topic, it would be greatly appreciated.



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