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SubjectRe: Page Faults slower in 2.6.25-rc9 than 2.6.23
On Tue, 29 Apr 2008, Ross Biro 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.

Do you have CONFIG_CGROUP_MEM_RES_CTLR=y in 2.6.25?
That added about 20% to my lmbench "Page Fault" tests (with
adverse effect on several others e.g. the fork, exec, sh group).

Try the same kernel with boot option "cgroup_disable=memory",
that should recoup most (but not quite all) of the slowdown;
or rebuild with n to CGROUP_MEM_RES_CTLR.

But your "Mmap Latency" went up 425% ??

Hugh

>
> 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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