Re: Performance regression in IO scheduler still there

[Jeff Moyer <jmoyer@redhat.com>]

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.

>>               2.6.29    2.6.32-rc6,low_latency=0
>> ----------------------------------
>> Average:      34.6648   34.4475
>> Pop.Std.Dev.: 0.55523   0.21981
>   Hmm, strange. Miklos Szeredi tried tiobench on his machine and he also
> saw the regression. I'll try to think what could make the difference.

OK, I'll try again.

Cheers,
Jeff