Re: Performance regression in IO scheduler still there

Jens Axboe
2009-11-12T21:00:00Z

On Thu, Nov 12 2009, Jeff Moyer wrote:
> Jan Kara <jack@suse.cz> writes:
>
> > On Wed 11-11-09 12:43:30, Jeff Moyer wrote:
> >> Jan Kara <jack@suse.cz> writes:
> >>
> >> > Sadly, I don't see the improvement you can see :(. The numbers are the
> >> > same regardless low_latency set to 0:
> >> > 2.6.32-rc5 low_latency = 0:
> >> > 37.39 36.43 36.51 -> 36.776667 0.434920
> >> > But my testing environment is a plain SATA drive so that probably
> >> > explains the difference...
> >>
> >> I just retested (10 runs for each kernel) on a SATA disk with no NCQ
> >> support and I could not see a difference. I'll try to dig up a disk
> >> that support NCQ. Is that what you're using for testing?
> > I don't think I am. How do I find out?
>
> Good question. ;-) I grep for NCQ in dmesg output and make sure it's
> greater than 0/32. There may be a better way, though.

cat /sys/block/<dev>/device/queue_depth

:-)

--
Jens Axboe