On Mon, May 21 2007, Alan D. Brunelle wrote:
> Jens Axboe wrote:
> >On Mon, May 21 2007, Alan D. Brunelle wrote:
> >
> >>Jens Axboe wrote:
> >>
> >>>On Tue, May 01 2007, Alan D. Brunelle wrote:
> >>>
> >>>
> >>>>Jens Axboe wrote:
> >>>>
> >>>>
> >>>>>On Mon, Apr 30 2007, Alan D. Brunelle wrote:
> >>>>>
> >>>>>
> >>>>>>The results from a single run of an AIM7 DBase load on a 16-way ia64
> >>>>>>box (64GB RAM + 144 FC disks) showed a slight regression (~0.5%) by
> >>>>>>adding in this patch. (Graph can be found at
> >>>>>>http://free.linux.hp.com/~adb/cfq/cfq_dbase.png ) It is only a
> >>>>>>single set of runs, on a single platform, but it is something to keep
> >>>>>>an eye on as the regression showed itself across the complete run.
> >>>>>>
> >>>>>>
> >>>>>Do you know if this regression is due to worse IO performance, or
> >>>>>increased system CPU usage?
> >>>>>
> >>>>>
> >>>>We performed two point runs yesterday (20,000 and 50,000 tasks) and
> >>>>here are the results:
> >>>>
> >>>>Kernel Tasks Jobs per Minute %sys (avg)
> >>>>------ ----- --------------- ----------
> >>>>2.6.21 20000 60,831.1 39.83%
> >>>>CFQ br 20000 60,237.4 40.80%
> >>>> -0.98% +2.44%
> >>>>
> >>>>2.6.21 50000 60,881.6 40.43%
> >>>>CFQ br 50000 60,400.6 40.80%
> >>>> -0.79% +0.92%
> >>>>
> >>>>So we're seeing a slight IO performance regression with a slight
> >>>>increase in %system with the CFQ branch. (A chart of the complete run
> >>>>values is up on http://free.linux.hp.com/~adb/cfq/cfq_20k50k.png ).
> >>>>
> >>>>
> >>>Alan, can you repeat that same run with this patch applied? It
> >>>reinstates the cfq lookup hash, which could account for increased system
> >>>utilization.
> >>>
> >>>
> >>Hi Jens -
> >>
> >>This test was performed over the weekend, results are updated on
> >>
> >>http://free.linux.hp.com/~adb/cfq/cfq_dbase.png
> >>
> >
> >Thanks a lot, Alan! So the cfq hash does indeed improve things a little,
> >that's a shame. I guess I'll just reinstate the hash lookup.
> >
> >
> You're welcome Jens, but remember: It's one set of data; from one
> benchmark; on one architecture; on one platform...don't know if you
> should scrap the whole thing for that! :-) At the very least, I could
> look into trying it out on another architecture. Let me see what I can
> dig up...
Of course it would be great if you could test on something else as well,
but I was aware that the cfq hash lookup could potentially cause a
performance degradation with some workloads. Your test shows about a
0.3% drop, which isn't a lot but still looks consistent. The cfq hash
code wasn't that complicated, so if it helps a bit, then I'm inclined to
put it back in.
Let me know if you can run it on something else!
--
Jens Axboe
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