Re: [PATCH 3/6] writeback: sync expired inodes first in background writeback

Wu Fengguang
2011-04-21T01:47:42Z

On Thu, Apr 21, 2011 at 09:01:32AM +0800, Dave Chinner wrote:
> On Wed, Apr 20, 2011 at 03:38:22PM +0800, Wu Fengguang wrote:
> > > make. Please test against a vanilla kernel if that is what you are
> > > aiming these patches for. If you aren't aiming for a vanilla kernel,
> > > please say so in the patch series header...
> >
> > Here are the test results for vanilla kernel. It's again shows better
> > numbers for dd, tar and overall run time.
> >
> > 2.6.39-rc3 2.6.39-rc3-dyn-expire+
> > ------------------------------------------------
> > all elapsed 256.043 252.367
> > stddev 24.381 12.530
> >
> > tar elapsed 30.097 28.808
> > dd elapsed 13.214 11.782
>
> The big reduction in run-to-run variance is very convincing - moreso
> than the reduction in runtime - That's kind of what I had hoped
> would occur once I understood the implications of the change. Thanks
> for running the test to close the loop. :)

And you can see how the user perceivable variations in elapsed time
are reduced by the patchsets:

vanilla
user system %cpu elapsed
stddev 0.000 0.037 0.539 0.805 dd, xfs
stddev 0.117 0.102 5.974 3.498 tar, xfs

moving-target
stddev 0.000 0.102 1.025 0.803 dd, xfs
stddev 0.131 0.136 4.415 2.136 tar, xfs

IO-less + moving-target
stddev 0.000 0.022 0.000 0.283 dd, xfs
stddev 0.000 0.031 0.000 0.151 dd, ext4
stddev 0.111 0.218 2.040 0.532 tar, xfs
stddev 0.129 0.119 1.020 0.215 tar, ext4

Thanks,
Fengguang