Re: ext4 write performance regression in 3.6-rc1 on RAID0/5

NeilBrown
2012-08-17T20:45:27Z

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On Fri, 17 Aug 2012 22:25:26 +0800 Fengguang Wu <fengguang.wu@intel.com>
wrote:

> [CC md list]
>
> On Fri, Aug 17, 2012 at 09:40:39AM -0400, Theodore Ts'o wrote:
> > On Fri, Aug 17, 2012 at 02:09:15PM +0800, Fengguang Wu wrote:
> > > Ted,
> > >
> > > I find ext4 write performance dropped by 3.3% on average in the
> > > 3.6-rc1 merge window. xfs and btrfs are fine.
> > >
> > > Two machines are tested. The performance regression happens in the
> > > lkp-nex04 machine, which is equipped with 12 SSD drives. lkp-st02 does
> > > not see regression, which is equipped with HDD drives. I'll continue
> > > to repeat the tests and report variations.
> >
> > Hmm... I've checked out the commits in "git log v3.5..v3.6-rc1 --
> > fs/ext4 fs/jbd2" and I don't see anything that I would expect would
> > cause that. The are the lock elimination changes for Direct I/O
> > overwrites, but that shouldn't matter for your tests which are
> > measuring buffered writes, correct?
> >
> > Is there any chance you could do me a favor and do a git bisect
> > restricted to commits involving fs/ext4 and fs/jbd2?
>
> I noticed that the regressions all happen in the RAID0/RAID5 cases.
> So it may be some interactions between the RAID/ext4 code?

I'm aware of some performance regression in RAID5 which I will be drilling
down into next week. Some things are faster, but some are slower :-(

RAID0 should be unchanged though - I don't think I've changed anything there.

Looking at your numbers, JBOD ranges from +6.5% to -1.5%
RAID0 ranges from +4.0% to -19.2%
RAID5 ranges from +20.7% to -39.7%

I'm guessing + is good and - is bad?
The RAID5 numbers don't surprise me. The RAID0 do.

>
> I'll try to get some ext2/3 numbers, which should have less changes on the fs side.

Thanks. That will be useful.

NeilBrown

>
> wfg@bee /export/writeback% ./compare -g ext4 lkp-nex04/*/*-{3.5.0,3.6.0-rc1+}
> 3.5.0 3.6.0-rc1+
> ------------------------ ------------------------
> 720.62 -1.5% 710.16 lkp-nex04/JBOD-12HDD-thresh=1000M/ext4-100dd-1-3.5.0
> 706.04 -0.0% 705.86 lkp-nex04/JBOD-12HDD-thresh=1000M/ext4-10dd-1-3.5.0
> 702.86 -0.2% 701.74 lkp-nex04/JBOD-12HDD-thresh=1000M/ext4-1dd-1-3.5.0
> 702.41 -0.0% 702.06 lkp-nex04/JBOD-12HDD-thresh=1000M/ext4-1dd-2-3.5.0
> 779.52 +6.5% 830.11 lkp-nex04/JBOD-12HDD-thresh=100M/ext4-100dd-1-3.5.0
> 646.70 +4.9% 678.59 lkp-nex04/JBOD-12HDD-thresh=100M/ext4-10dd-1-3.5.0
> 704.49 +2.6% 723.00 lkp-nex04/JBOD-12HDD-thresh=100M/ext4-1dd-1-3.5.0
> 704.21 +1.2% 712.47 lkp-nex04/JBOD-12HDD-thresh=100M/ext4-1dd-2-3.5.0
> 705.26 -1.2% 696.61 lkp-nex04/JBOD-12HDD-thresh=8G/ext4-100dd-1-3.5.0
> 703.37 +0.1% 703.76 lkp-nex04/JBOD-12HDD-thresh=8G/ext4-10dd-1-3.5.0
> 701.66 -0.1% 700.83 lkp-nex04/JBOD-12HDD-thresh=8G/ext4-1dd-1-3.5.0
> 701.17 +0.0% 701.36 lkp-nex04/JBOD-12HDD-thresh=8G/ext4-1dd-2-3.5.0
> 675.08 -10.5% 604.29 lkp-nex04/RAID0-12HDD-thresh=1000M/ext4-100dd-1-3.5.0
> 676.52 -2.7% 658.38 lkp-nex04/RAID0-12HDD-thresh=1000M/ext4-10dd-1-3.5.0
> 512.70 +4.0% 533.22 lkp-nex04/RAID0-12HDD-thresh=1000M/ext4-1dd-1-3.5.0
> 524.61 -0.3% 522.90 lkp-nex04/RAID0-12HDD-thresh=1000M/ext4-1dd-2-3.5.0
> 709.76 -15.7% 598.44 lkp-nex04/RAID0-12HDD-thresh=100M/ext4-100dd-1-3.5.0
> 681.39 -2.1% 667.25 lkp-nex04/RAID0-12HDD-thresh=100M/ext4-10dd-1-3.5.0
> 524.16 +0.8% 528.25 lkp-nex04/RAID0-12HDD-thresh=100M/ext4-1dd-2-3.5.0
> 699.77 -19.2% 565.54 lkp-nex04/RAID0-12HDD-thresh=8G/ext4-100dd-1-3.5.0
> 675.79 -1.9% 663.17 lkp-nex04/RAID0-12HDD-thresh=8G/ext4-10dd-1-3.5.0
> 484.84 -7.4% 448.83 lkp-nex04/RAID0-12HDD-thresh=8G/ext4-1dd-1-3.5.0
> 470.40 -3.2% 455.31 lkp-nex04/RAID0-12HDD-thresh=8G/ext4-1dd-2-3.5.0
> 167.97 -38.7% 103.03 lkp-nex04/RAID5-12HDD-thresh=1000M/ext4-100dd-1-3.5.0
> 243.67 -9.1% 221.41 lkp-nex04/RAID5-12HDD-thresh=1000M/ext4-10dd-1-3.5.0
> 248.98 +12.2% 279.33 lkp-nex04/RAID5-12HDD-thresh=1000M/ext4-1dd-1-3.5.0
> 208.45 +14.1% 237.86 lkp-nex04/RAID5-12HDD-thresh=1000M/ext4-1dd-2-3.5.0
> 71.18 -34.2% 46.82 lkp-nex04/RAID5-12HDD-thresh=100M/ext4-100dd-1-3.5.0
> 145.84 -7.3% 135.25 lkp-nex04/RAID5-12HDD-thresh=100M/ext4-10dd-1-3.5.0
> 255.22 +6.7% 272.35 lkp-nex04/RAID5-12HDD-thresh=100M/ext4-1dd-1-3.5.0
> 243.09 +20.7% 293.30 lkp-nex04/RAID5-12HDD-thresh=100M/ext4-1dd-2-3.5.0
> 209.24 -23.6% 159.96 lkp-nex04/RAID5-12HDD-thresh=8G/ext4-100dd-1-3.5.0
> 243.73 -10.9% 217.28 lkp-nex04/RAID5-12HDD-thresh=8G/ext4-10dd-1-3.5.0
> 214.25 +5.6% 226.32 lkp-nex04/RAID5-12HDD-thresh=8G/ext4-1dd-1-3.5.0
> 207.16 +13.4% 234.98 lkp-nex04/RAID5-12HDD-thresh=8G/ext4-1dd-2-3.5.0
> 17572.12 -1.9% 17240.05 TOTAL write_bw
>
> Thanks,
> Fengguang

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