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SubjectRe: Page Faults slower in 2.6.25-rc9 than 2.6.23
On Tue, 29 Apr 2008 09:10:36 -0400
"Ross Biro" <rossb@google.com> wrote:

> I don't know if this has been noticed before. I was benchmarking my
> page table relocation code and I noticed that on 2.6.25-rc9 page
> faults take 10% more time than on 2.6.22. This is using lmbench
> running on an intel x86_64 system. The good news is that the page
> table relocation code now only adds a 1.6% slow down to page faults.
>

It seems lmbench's pagefault program uses 'page fault by READ'.
Then, this patch affects. (this patch was added at 2.6.24-rc?.)
==
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=557ed1fa2620dc119adb86b34c614e152a629a80
==
By it, ZERO_PAGE is not used for page fault in anonymous mapping.
So it seems an expexted result.

Thanks,
-Kame

> Ross
>
> 2.6.25-rc9:
>
> File & VM system latencies in microseconds - smaller is better
> -------------------------------------------------------------------------------
> Host OS 0K File 10K File Mmap Prot Page 100fd
> Create Delete Create Delete Latency Fault Fault selct
> --------- ------------- ------ ------ ------ ------ ------- ----- ------- -----
> ipnn2 Linux 2.6.25- 13.9 7.6111 103.4 9.7453 926.0 0.711 2.14250 2.552
> ipnn2 Linux 2.6.25- 13.7 7.6243 310.7 9.6574 932.0 0.750 2.15970 2.555
> ipnn2 Linux 2.6.25- 13.9 7.6831 192.5 10.0 927.0 0.760 2.21310 2.553
> ipnn2 Linux 2.6.25- 13.9 7.5739 98.4 9.5330 927.0 0.703 2.17610 2.554
> ipnn2 Linux 2.6.25- 14.6 7.6429 39.1 10.8 935.0 0.763 2.17250 2.552
> ipnn2 Linux 2.6.25- 14.1 7.8777 129.8 9.9375 930.0 0.782 2.26460 2.559
> ipnn2 Linux 2.6.25- 14.8 7.9639 623.8 8.2042 927.0 0.773 2.21510 2.557
> ipnn2 Linux 2.6.25- 14.4 7.5842 622.3 8.3272 920.0 0.745 2.22210 2.558
> ipnn2 Linux 2.6.25- 14.2 7.6339 45.7 10.2 935.0 0.675 2.23860 2.554
> ipnn2 Linux 2.6.25- 14.1 7.7175 263.7 10.1 929.0 0.762 2.22350 2.556
> ipnn2 Linux 2.6.25- 13.9 8.1230 378.2 9.4343 975.0 0.752 2.25920 2.554
>
>
> 2.6.23:
> File & VM system latencies in microseconds - smaller is better
> -------------------------------------------------------------------------------
> Host OS 0K File 10K File Mmap Prot Page 100fd
> Create Delete Create Delete Latency Fault Fault selct
> --------- ------------- ------ ------ ------ ------ ------- ----- ------- -----
> ipnn2 Linux 2.6.23- 218.0 0.912 1.94010 2.626
> ipnn2 Linux 2.6.23- 219.0 1.095 1.96400 2.597
> ipnn2 Linux 2.6.23- 219.0 0.774 1.96640 2.603
> ipnn2 Linux 2.6.23- 221.0 0.946 1.99950 2.601
> ipnn2 Linux 2.6.23- 219.0 0.902 1.99160 2.733
> ipnn2 Linux 2.6.23- 217.0 0.904 2.04790 2.601
> ipnn2 Linux 2.6.23- 225.0 0.893 1.99620 2.600
>
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