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SubjectRe: Cfq first request patch changes IO performance
On Mon, Feb 26 2007, Ananiev, Leonid I wrote:
> The patch "cfq-iosched: defer slice activation to first request being
> active"
> http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=c
> ommitdiff;h=44f7c16065c83060cbb9dd9b367141682a6e2b8e;hp=99f9628aba4d8fb3
> b8d955c9efded0d0a1995fad
>
> Sysbench fileio (random read/write mix) -15%
> Tiobench sequential write -3%
> Tiobench random write -5%
> Iozone record re-write -21%
> Iozone mmap sequential read -20%
> Iozone mmap random write +45%
> Aio-stress direct sequential read +29%
> For other 3 tiobench, 7 aiostress and 13 iozone tests the result changes
> are less than variation.
>
> Considered patch does not impact on performance if all threads have
> equal IO activity (tiobench).
> If single thread has IO activity the performance becomes unstable and is
> decreased mainly.

Yep there are a few unfortunate side effects, I have later fixed those.
I just need to split that patchset up and commit it.

--
Jens Axboe

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