Re: More io-cpu-affinity results: queue_affinity + rq_affinity

Alan D. Brunelle
2008-05-05T12:46:32Z

Alan D. Brunelle wrote:
> Continuing to evaluate the potential benefits of the various I/O & CPU
> affinity options proposed in Jens' origin/io-cpu-affinity branch...
>
> Executive summary (due to the rather long-winded nature of this post):
>
> We again see rq_affinity has positive potential, but not (yet) able to
> see much benefit to adjusting queue_affinity.
>
> ========================================================
>
<snip>
>
> =====================================================
>
> As noted above, I'm going to do a series of runs to make sure this data
> holds over a larger data set (in particular the case where I/O is far -
> looking at QAF on & far to see if the 0.56% is truly representative).
> Suggestions for other tests to try and show/determine queue_affinity
> benefits are very welcome.

The averages (+ min/max error bars) for the reads/second & p_system
values when taken over 50 runs of the test can be seen at:

http://free.linux.hp.com/~adb/jens/r_s_50.png

and

http://free.linux.hp.com/~adb/jens/p_system_50.png

respectively. Still shows a potential big win w/ rq_affinity set to 1,
not much difference at all w/ queue_affinity settings (in fact, not
seeing any real movement at all when rq_affinity=1).

I'd still be willing to try other test scenarios to show how
queue_affinity can really help, but as for now, I'd suggest removing
that functionality for the present - getting rid of some code until such
time as we can prove its worth.

Alan