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

[Balbir Singh <balbir linux vnet ibm com>]

* Vivek Goyal <vgoyal redhat com> [2009-06-22 13:08:12]:

> On Mon, Jun 22, 2009 at 12:06:42PM -0400, Jeff Moyer wrote:
> > Vivek Goyal <vgoyal redhat com> writes:
> > 
> > > 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?
> > 
> > O_DIRECT bypasses the page cache, and hence the readahead code.  Try
> > driving deeper queue depths and/or using larger I/O sizes.
> 
> Ok. Thanks. I tried increasing iodepth to 20 and it helped a lot.
> 
> test1 statistics: time=8 16 6672   sectors=8 16 1049656
> test2 statistics: time=8 16 3508   sectors=8 16 583432
>

Good to see.. Thanks! 

-- 
	Balbir