Re: Transparent Hugepage impact on memcpy

[Hush Bensen <hush.bensen@gmail.com>]

Cc thp guys.

ao? 2013/6/4 16:57, Jianguo Wu a??e??:
> Hi all,
>
> I tested memcpy with perf bench, and found that in prefault case, When Transparent Hugepage is on,
> memcpy has worse performance.
>
> When THP on is 3.672879 GB/Sec (with prefault), while THP off is 6.190187 GB/Sec (with prefault).
>
> I think THP will improve performance, but the test result obviously not the case.
> Andrea mentioned THP cause "clear_page/copy_page less cache friendly" in
> http://events.linuxfoundation.org/slides/2011/lfcs/lfcs2011_hpc_arcangeli.pdf.
>
> I am not quite understand this, could you please give me some comments, Thanks!
>
> I test in Linux-3.4-stable, and my machine info is:
> Intel(R) Xeon(R) CPU           E5520  @ 2.27GHz
>
> available: 2 nodes (0-1)
> node 0 cpus: 0 1 2 3 8 9 10 11
> node 0 size: 24567 MB
> node 0 free: 23550 MB
> node 1 cpus: 4 5 6 7 12 13 14 15
> node 1 size: 24576 MB
> node 1 free: 23767 MB
> node distances:
> node   0   1
>    0:  10  20
>    1:  20  10
>
> Below is test result:
> ---with THP---
> #cat /sys/kernel/mm/transparent_hugepage/enabled
> [always] madvise never
> #./perf bench mem memcpy -l 1gb -o
> # Running mem/memcpy benchmark...
> # Copying 1gb Bytes ...
>
>         3.672879 GB/Sec (with prefault)
>
> #./perf stat ...
> Performance counter stats for './perf bench mem memcpy -l 1gb -o':
>
>            35455940 cache-misses              #   53.504 % of all cache refs     [49.45%]
>            66267785 cache-references                                             [49.78%]
>                2409 page-faults
>           450768651 dTLB-loads
>                                                    [50.78%]
>               24580 dTLB-misses
>                #    0.01% of all dTLB cache hits  [51.01%]
>          1338974202 dTLB-stores
>                                                   [50.63%]
>               77943 dTLB-misses
>                                                   [50.24%]
>           697404997 iTLB-loads
>                                                    [49.77%]
>                 274 iTLB-misses
>                #    0.00% of all iTLB cache hits  [49.30%]
>
>         0.855041819 seconds time elapsed
>
> ---no THP---
> #cat /sys/kernel/mm/transparent_hugepage/enabled
> always madvise [never]
>
> #./perf bench mem memcpy -l 1gb -o
> # Running mem/memcpy benchmark...
> # Copying 1gb Bytes ...
>
>         6.190187 GB/Sec (with prefault)
>
> #./perf stat ...
> Performance counter stats for './perf bench mem memcpy -l 1gb -o':
>
>            16920763 cache-misses              #   98.377 % of all cache refs     [50.01%]
>            17200000 cache-references                                             [50.04%]
>              524652 page-faults
>           734365659 dTLB-loads
>                                                    [50.04%]
>             4986387 dTLB-misses
>                #    0.68% of all dTLB cache hits  [50.04%]
>          1013408298 dTLB-stores
>                                                   [50.04%]
>             8180817 dTLB-misses
>                                                   [49.97%]
>          1526642351 iTLB-loads
>                                                    [50.41%]
>                  56 iTLB-misses
>                #    0.00% of all iTLB cache hits  [50.21%]
>
>         1.025425847 seconds time elapsed
>
> Thanks,
> Jianguo Wu.
>
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