* Kristian Benoit <[email protected]> wrote:
> This is the 3rd run of our tests.
i'm still having problems reproducing your numbers, even the 'plain'
ones. I cannot even get the same ballpark figures, on 3 separate
systems. To pick one number:
> "plain" run:
>
> Measurements | Vanilla | preemp_rt |
> ---------------+-------------+----------------+
> mmap | 660us | 2867us (+334%) |
i was unable to reproduce this level of lat_mmap degradation. I do
indeed see a slowdown [*], but nowhere near the 4.3x slowdown measured
here. I have tried the very lmbench version you used (2.0.4) on 3
different systems (Athlon64 2GHz, Celeron 466MHz, Xeon 2.4GHz - the last
one should be pretty similar to your 2.8GHz Xeon testbox) and neither
showed this level of slowdown.
i couldnt figure out which precise options were used by your test,
because i only found the summary lmbench page of one of the older tests
- so i did my lat_mmap testing with various sizes: 10MB, 30MB, 70MB,
150MB, 200MB, 500MB. (My best guess would be that since your target box
has 512MB of RAM, lmbench will pick an mmap-file size of 144 MB. Or if
it's the 256MB box, lmbench will pick roughly 70 MB. I covered those
likely sizes too.) Neither size showed this level of slowdown.
so my tentative conclusion would be that the -RT kernel is still
misconfigured somehow. Did you have HIGHMEM64 and HIGHPTE enabled
perhaps? Those i suggested to be turned off in one of my first mails to
you, it is something that will cause bad performance under PREEMPT_RT.
(Highmem64 is unwarranted for an embedded test anyway - it's only needed
to support more than 4 GB of RAM.) Could you send me the test 3 .config
you used on the -RT kernel?
Ingo
[*] fixed in -50-36 and later PREEMPT_RT kernels
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