From: Shaohua Li Subject: Re: ext4 write performance regression in 3.6-rc1 on RAID0/5 Date: Wed, 22 Aug 2012 12:07:26 +0800 Message-ID: <50345AFE.1070700@fusionio.com> References: <20120816024654.GB3781@thunk.org> <20120816111051.GA16036@localhost> <20120816152513.GA31346@thunk.org> <20120817060915.GB28786@localhost> <20120817134039.GB11439@thunk.org> <20120817142526.GA1059@localhost> <20120822035702.GF2570@yliu-dev.sh.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Cc: Fengguang Wu , NeilBrown , Theodore Ts'o , Marti Raudsepp , Kernel hackers , ext4 hackers , "maze@google.com" , "Shi, Alex" , "linux-fsdevel@vger.kernel.org" , linux RAID To: Yuanhan Liu Return-path: In-Reply-To: <20120822035702.GF2570@yliu-dev.sh.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On 8/22/12 11:57 AM, Yuanhan Liu wrote: > On Fri, Aug 17, 2012 at 10:25:26PM +0800, Fengguang Wu 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'll try to get some ext2/3 numbers, which should have less changes on the fs side. > > > > 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 > > Hi, > > About this issue, I did some investigation. And found we are blocked at > get_active_stripes() in most times. It's reasonable, since max_nr_stripes > is set to 256 now. It's a kind of small value, thus I tried with > different value. Please see the following patch for detailed numbers. > > The test machine is same as above. > > From 85c27fca12b770da5bc8ec9f26a22cb414e84c68 Mon Sep 17 00:00:00 2001 > From: Yuanhan Liu > Date: Wed, 22 Aug 2012 10:51:48 +0800 > Subject: [RFC PATCH] md/raid5: increase NR_STRIPES to 1024 > > Stripe head is a must held resource before doing any IO. And it's > limited to 256 by default. With 10dd case, we found that it is > blocked at get_active_stripes() in most times(please see the ps > output attached). > > Thus I did some tries with different value set to NR_STRIPS, and > here are some numbers(EXT4 only) I got with different NR_STRIPS set: > > write bandwidth: > ================ > 3.5.0-rc1-256+: (Here 256 means with max strip head set to 256) > write bandwidth: 280 > 3.5.0-rc1-1024+: > write bandwidth: 421 (+50.4%) > 3.5.0-rc1-4096+: > write bandwidth: 506 (+80.7%) > 3.5.0-rc1-32768+: > write bandwidth: 615 (+119.6%) > > (Here 'sh' means with Shaohua's "multiple threads to handle strips" patch [0]) > 3.5.0-rc3-strip-sh+-256: > write bandwidth: 465 > > 3.5.0-rc3-strip-sh+-1024: > write bandwidth: 599 > > 3.5.0-rc3-strip-sh+-32768: > write bandwidth: 615 > > The kernel maybe a bit older but I found that the data are still kind of > valid. Though, I haven't tried Shaohua's latest patch. > > As you can see from those data above: the write bandwidth is increased > (a lot) as we increase NR_STRIPES. Thus the bigger NR_STRIPES set, the > better write bandwidth we get. But we can't set NR_STRIPES with a too > large number, especially by default, or it need lots of memory. Due to > the number I got with Shaohua's patch applied, I guess 1024 would be > nice value; it's not too big but we gain above 110% performance. > > Comments? BTW, I have a more flexible(more stupid, in the meantime) way: > change the max_nr_stripes dynamically based on need? > > Here I also attached more data: the script I used to get those number, > ps output, and iostat -kx 3 output. > > The script does it's job in a straight way: start NR dd in background, > trace the writeback/global_dirty_state event in background to count the > write bandwidth, sample the ps out regularly. > > --- > [0]: patch: http://lwn.net/Articles/500200/ > > Signed-off-by: Yuanhan Liu > --- > drivers/md/raid5.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c > index adda94d..82dca53 100644 > --- a/drivers/md/raid5.c > +++ b/drivers/md/raid5.c > @@ -62,7 +62,7 @@ > * Stripe cache > */ > > -#define NR_STRIPES 256 > +#define NR_STRIPES 1024 > #define STRIPE_SIZE PAGE_SIZE > #define STRIPE_SHIFT (PAGE_SHIFT - 9) > #define STRIPE_SECTORS (STRIPE_SIZE>>9) does revert commit 8811b5968f6216e fix the problem? Thanks, Shaohua