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    SubjectRe: Performance regression in IO scheduler still there
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    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


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