On Mon, Feb 26 2007, Suparna Bhattacharya wrote:
> On Mon, Feb 26, 2007 at 02:57:36PM +0100, Jens Axboe wrote:
> >
> > Some more results, using a larger number of processes and io depths. A
> > repeat of the tests from friday, with added depth 20000 for syslet and
> > libaio:
> >
> > Engine Depth Processes Bw (MiB/sec)
> > ----------------------------------------------------
> > libaio 1 1 602
> > syslet 1 1 759
> > sync 1 1 776
> > libaio 32 1 832
> > syslet 32 1 898
> > libaio 20000 1 581
> > syslet 20000 1 609
> >
> > syslet still on top. Measuring O_DIRECT reads (of 4kb size) on ramfs
> > with 100 processes each with a depth of 200, reading a per-process
> > private file of 10mb (need to fit in my ram...) 10 times each. IOW,
> > doing 10,000MiB of IO in total:
>
> But, why ramfs ? Don't we want to exercise the case where O_DIRECT actually
> blocks ? Or am I missing something here ?
Just overhead numbers for that test case, lets try something like your
described job.
Test case is doing random reads from /dev/sdb, in chunks of 64kb:
Engine Depth Processes Bw (KiB/sec)
----------------------------------------------------
libaio 200 100 2813
syslet 200 100 3944
libaio 20000 1 2793
syslet 20000 1 3854
sync (*) 20000 1 2866
deadline was used for IO scheduling, to minimize impact. Not sure why
syslet actually does so much better here, looing at vmstat the rate is
steady and all runs are basically 50/50 idle/wait. One difference is
that the submission itself takes a long time on libaio, since the
io_submit() will block on request allocation. The generated IO pattern
from each process is the same for all runs. The drive is a lousy sata
that doesn't even do queuing, FWIW.
[*] Just for comparison, the depth is obviously really 1 at the kernel
side since it's sync.
--
Jens Axboe
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