Re: [PATCH 1/2] writeback: Improve busyloop prevention

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  Hello Fengguang,

On Mon 05-12-11 16:02:43, Wu Fengguang wrote:
> On Thu, Nov 10, 2011 at 10:50:44PM +0800, Jan Kara wrote:
> > On Wed 09-11-11 00:52:07, Jan Kara wrote:
> > > > wfg@bee /export/writeback% ./compare.rb -v jsize -e io_wkB_s thresh*/*-ioless-full-next-20111102+ thresh*/*-20111102+
> > > > 3.1.0-ioless-full-next-20111102+  3.1.0-ioless-full-bg-all-next-20111102+
> > > > ------------------------  ------------------------
> > > >                 36231.89        -3.8%     34855.10  thresh=1000M/ext3-100dd-4k-8p-4096M-1000M:10-X
> > > >                 41115.07       -12.7%     35886.36  thresh=1000M/ext3-10dd-4k-8p-4096M-1000M:10-X
> > > >                 48025.75       -14.3%     41146.57  thresh=1000M/ext3-1dd-4k-8p-4096M-1000M:10-X
> > > >                 47684.35        -6.4%     44644.30  thresh=1000M/ext4-100dd-4k-8p-4096M-1000M:10-X
> > > >                 54015.86        -4.0%     51851.01  thresh=1000M/ext4-10dd-4k-8p-4096M-1000M:10-X
> > > >                 55320.03        -2.6%     53867.63  thresh=1000M/ext4-1dd-4k-8p-4096M-1000M:10-X
> > > >                 37400.51        +1.6%     38012.57  thresh=100M/ext3-10dd-4k-8p-4096M-100M:10-X
> > > >                 45317.31        -4.5%     43272.16  thresh=100M/ext3-1dd-4k-8p-4096M-100M:10-X
> > > >                 40552.64        +0.8%     40884.60  thresh=100M/ext3-2dd-4k-8p-4096M-100M:10-X
> > > >                 44271.29        -5.6%     41789.76  thresh=100M/ext4-10dd-4k-8p-4096M-100M:10-X
> > > >                 54334.22        -3.5%     52435.69  thresh=100M/ext4-1dd-4k-8p-4096M-100M:10-X
> > > >                 52563.67        -6.1%     49341.84  thresh=100M/ext4-2dd-4k-8p-4096M-100M:10-X
> > > >                 45027.95        -1.0%     44599.37  thresh=10M/ext3-1dd-4k-8p-4096M-10M:10-X
> > > >                 42478.40        +0.3%     42608.48  thresh=10M/ext3-2dd-4k-8p-4096M-10M:10-X
> > > >                 35178.47        -0.2%     35103.56  thresh=10M/ext4-10dd-4k-8p-4096M-10M:10-X
> > > >                 54079.64        -0.5%     53834.85  thresh=10M/ext4-1dd-4k-8p-4096M-10M:10-X
> > > >                 49982.11        -0.4%     49803.44  thresh=10M/ext4-2dd-4k-8p-4096M-10M:10-X
> > > >                783579.17        -3.8%    753937.28  TOTAL io_wkB_s
> > >   Here I can see some noticeable drops in the realistic thresh=100M case
> > > (case thresh=1000M is unrealistic but it still surprise me that there are
> > > drops as well). I'll try to reproduce your results so that I can look into
> > > this more effectively.
> >   So I've run a test on a machine with 1G of memory, thresh=184M (so
> > something similar to your 4G-1G test). I've used tiobench using 10 threads,
> > each thread writing 1.6G file. I have run the test 10 times to get an idea
> > of fluctuations. The result is:
> >   without patch			with patch
> >    AVG         STDDEV      AVG         STDDEV
> > 199.884820 +- 1.32268	200.466003 +- 0.377405
> > 
> > The numbers are time-to-completion so lower is better. Summary is: No
> > statistically meaningful difference. I'll run more tests with different
> > dirty thresholds to see whether I won't be able to observe some
> > difference...
> 
> I carried out some tests on ext3/ext4 before/after patch. Most tests
> are repeated for 3 times so as to get an idea about the variations.
> 
> The ":jsize=8" notion means "-J size=8" in action.
> 
> The overall deltas are -0.3% for ext4 and -3.3% for ext3.  I noticed
> that the regressions mostly happen for the "-J size=8" cases.  For
> normal mkfs, ext4 actually sees +2.5% increase and ext3 sees only
> -0.8% drop.
> 
> I don't find any misbehaves in the graphs.
> So in general I think the test results are acceptable.
  Thanks for running the tests. I looked through the results and given the
variation I would be happy with them. Will you merge the patch or should I
resend it?

								Honza

-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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