On Tue, Jun 04, 2013 at 04:57:57PM +0800, Jianguo Wu wrote:
>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 get similar result as you against 3.10-rc4 in the attachment. This
dues to the characteristic of thp takes a single page fault for each 
2MB virtual region touched by userland.

>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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