On Wed, Sep 26 2007, Alan D. Brunelle wrote:
> Mathieu Desnoyers wrote:
>> * Alan D. Brunelle ([email protected]) wrote:
>>> Taking Linux 2.6.23-rc6 + 2.6.23-rc6-mm1 as a basis, I took some sample
>>> runs of the following on both it and after applying Mathieu Desnoyers
>>> 11-patch sequence (19 September 2007).
>>>
>>> * 32-way IA64 + 132GiB + 10 FC adapters + 10 HP MSA 1000s (one 72GiB
>>> volume per MSA used)
>>>
>>> * 10 runs with each configuration, averages shown below
>>> o 2.6.23-rc6 + 2.6.23-rc6-mm1 without blktrace running
>>> o 2.6.23-rc6 + 2.6.23-rc6-mm1 with blktrace running
>>> o 2.6.23-rc6 + 2.6.23-rc6-mm1 + markers without blktrace running
>>> o 2.6.23-rc6 + 2.6.23-rc6-mm1 + markers with blktrace running
>>>
>>> * A run consists of doing the following in parallel:
>>> o Make an ext3 FS on each of the 10 volumes
>>> o Mount & unmount each volume
>>> + The unmounting generates a tremendous amount of writes
>>> to the disks - thus stressing the intended storage
>>> devices (10 volumes) plus the separate volume for all
>>> the blktrace data (when blk tracing is enabled).
>>> + Note the times reported below only cover the
>>> make/mount/unmount time - the actual blktrace runs
>>> extended beyond the times measured (took quite a while
>>> for the blk trace data to be output). We're only
>>> concerned with the impact on the "application"
>>> performance in this instance.
>>>
>>> Results are:
>>>
>>> Kernel w/out BT STDDEV w/ BT
>>> STDDEV
>>> ------------------------------------- --------- ------ ---------
>>> ------
>>> 2.6.23-rc6 + 2.6.23-rc6-mm1 14.679982 0.34 27.754796
>>> 2.09
>>> 2.6.23-rc6 + 2.6.23-rc6-mm1 + markers 14.993041 0.59 26.694993
>>> 3.23
>>>
>>
>> Interesting results, although we cannot say any of the solutions has much
>> impact due to the std dev.
>>
>> Also, it could be interesting to add the "blktrace compiled out" as a
>> base line.
>>
>> Thanks for running those tests,
>>
>> Mathieu
> Mathieu:
>
> Here are the results from 6 different kernels (including ones with blktrace
> not configured in), with now performing 40 runs per kernel.
>
> o All kernels start off with Linux 2.6.23-rc6 + 2.6.23-rc6-mm1
>
> o '- bt cfg' or '+ bt cfg' means a kernel without or with blktrace
> configured respectively.
>
> o '- markers' or '+ markers' means a kernel without or with the 11-patch
> marker series respectively.
>
> 38 runs without blk traces being captured (dropped hi/lo value from 40
> runs)
>
> Kernel Options Min val Avg val Max val Std Dev
> ------------------ --------- --------- --------- ---------
> - markers - bt cfg 15.349127 16.169459 16.372980 0.184417
> + markers - bt cfg 15.280382 16.202398 16.409257 0.191861
>
> - markers + bt cfg 14.464366 14.754347 16.052306 0.463665
> + markers + bt cfg 14.421765 14.644406 15.690871 0.233885
>
> 38 runs with blk traces being captured (dropped hi/lo value from 40 runs)
>
> Kernel Options Min val Avg val Max val Std Dev
> ------------------ --------- --------- --------- ---------
> - markers + bt cfg 24.675859 28.480446 32.571484 1.713603
> + markers + bt cfg 18.713280 27.054927 31.684325 2.857186
>
> o It is not at all clear why running without blk trace configured into
> the kernel runs slower than with blk trace configured in. (9.6 to 10.6%
> reduction)
> o The data is still not conclusive with respect to whether the marker
> patches change performance characteristics when we're not gathering traces.
> It appears
> that any change in performance is minimal at worst for this test.
> o The data so far still doesn't conclusively show a win in this case
> even when we are capturing traces, although, the average certainly seems to
> be in its favor.
> One concern that I should be able to deal easily with is the choice of
> the IO scheduler being used for both the volume being used to perform the
> test on, as well as the one used for storing blk traces (when enabled).
> Right now I was using the default CFQ, when perhaps NOOP or DEADLINE would
> be a better choice. If there is enough interest in seeing how that changes
> things I could try to get some runs in later this week.
Alan,
Thanks for running these numbers as well. I don't think you have to
bother with it more. My main concern was a performance regression,
increasing the overhead of running blktrace. So while we (well, you :-))
could run more tests, I'd say the above is Good Enough for me. Mathieu,
you can add my Acked-by: Jens Axboe <[email protected]> to the
blktrace part of your marker series.
I do wonder about that performance _increase_ with blktrace enabled. I
remember that we have seen and discussed something like this before,
it's still a puzzle to me...
--
Jens Axboe
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