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[dm-devel] Re: [RFC] IO scheduler based io controller (V5)



On Mon, Jun 22, 2009 at 11:40:42AM -0400, Jeff Moyer wrote:
> Vivek Goyal <vgoyal redhat com> writes:
> 
> > On Sun, Jun 21, 2009 at 08:51:16PM +0530, Balbir Singh wrote:
> >> * Vivek Goyal <vgoyal redhat com> [2009-06-19 16:37:18]:
> >> 
> >> > 
> >> > Hi All,
> >> > 
> >> > Here is the V5 of the IO controller patches generated on top of 2.6.30.
> >> [snip]
> >> 
> >> > Testing
> >> > =======
> >> >
> >> 
> >> [snip]
> >> 
> >> I've not been reading through the discussions in complete detail, but
> >> I see no reference to async reads or aio. In the case of aio, aio
> >> presumes the context of the user space process. Could you elaborate on
> >> any testing you've done with these cases? 
> >> 
> >
> > Hi Balbir,
> >
> > So far I had not done any testing with AIO. I have done some just now.
> > Here are the results.
> >
> > Test1 (AIO reads)
> > ================
> > Set up two fio, AIO read jobs in two cgroup with weight 1000 and 500
> > respectively. I am using cfq scheduler. Following are some lines from my test
> > script.
> >
> > ===================================================================
> > fio_args="--ioengine=libaio --rw=read --size=512M"
> 
> AIO doesn't make sense without O_DIRECT.
> 

Ok, here are the read results with --direct=1 for reads. In previous posting,
writes were already direct.

test1 statistics: time=8 16 20796   sectors=8 16 1049648
test2 statistics: time=8 16 10551   sectors=8 16 581160


Not sure why reads are so slow with --direct=1? In the previous test
(no direct IO), I had cleared the caches using
(echo 3 > /proc/sys/vm/drop_caches) so reads could not have come from page
cache?

Thanks
Vivek


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