Date:   Thu, 21 Jul 2022 13:03:35 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Lukas Czerner <lczerner@...hat.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Benjamin Coddington <bcodding@...hat.com>
Subject: Re: should we make "-o iversion" the default on ext4 ?

On Thu, 2022-07-21 at 16:06 +0200, Lukas Czerner wrote:
> On Wed, Jul 20, 2022 at 12:42:11PM -0400, Jeff Layton wrote:
> > On Wed, 2022-07-20 at 17:22 +0200, Lukas Czerner wrote:
> > 
> > >  But not zero, at least
> > > every time the inode is loaded from disk it is scheduled for i_version
> > > update on the next attempted increment. Could that have an effect on
> > > some particular common workload you can think of?
> > > 
> > 
> > FWIW, it's doubtful that you'd even notice this. You'd almost certainly
> > be updating the mtime or ctime on the next change anyway, so updating
> > the i_version in that case is basically free. You will probably need to
> > do some a few extra atomic in-memory operations, but that's probably not
> > noticeable in something I/O constrained.
> > 
> > > 
> > > Could you provide some performance numbers for iversion case?
> > > 
> > 
> > I'm writing to a LVM volume on a no-name-brand ssd I have sitting
> > around. fio jobfile is here:
> 
> That's very simplistic test, but fair enough. I've ran 10 iterations of
> xfstests with and without iversion and there is no significant
> difference, in fact it's all well within run by run variation. That's
> true in aggregate as well for individual tests.
> 

Yeah. This change was most evident with small I/O sizes, so if there is
an effect here it'll likely show up there.
 
> However there are problems to solve before we attempt to make it a
> default. With -o iversion ext4/026 and generic/622 fails. The ext4/026
> seems to be a real bug and I am not sure about the other one yet.
> 
> I'll look into it.
> 

Interesting, thanks. Lack of testing with that option enabled is
probably another good reason to go ahead and make it the default. Let me
know what you find.

> -Lukas
> 
> > 
> > [global]
> > name=fio-seq-write
> > filename=fio-seq-write
> > rw=write
> > bs=4k
> > direct=0
> > numjobs=1
> > time_based
> > runtime=300
> > 
> > [file1]
> > size=1G
> > ioengine=libaio
> > iodepth=16
> > 
> > iversion support disabled:
> > 
> > $ fio ./4k-write.fio
> > file1: (g=0): rw=write, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=16
> > fio-3.27
> > Starting 1 process
> > file1: Laying out IO file (1 file / 1024MiB)
> > Jobs: 1 (f=1): [W(1)][100.0%][w=52.5MiB/s][w=13.4k IOPS][eta 00m:00s]
> > file1: (groupid=0, jobs=1): err= 0: pid=10056: Wed Jul 20 12:28:21 2022
> >   write: IOPS=96.3k, BW=376MiB/s (394MB/s)(110GiB/300001msec); 0 zone resets
> >     slat (nsec): min=1112, max=5727.5k, avg=1917.70, stdev=1300.30
> >     clat (nsec): min=1112, max=2146.5M, avg=156067.38, stdev=15568002.13
> >      lat (usec): min=3, max=2146.5k, avg=158.03, stdev=15568.00
> >     clat percentiles (usec):
> >      |  1.00th=[   36],  5.00th=[   36], 10.00th=[   37], 20.00th=[   37],
> >      | 30.00th=[   38], 40.00th=[   38], 50.00th=[   38], 60.00th=[   39],
> >      | 70.00th=[   39], 80.00th=[   40], 90.00th=[   42], 95.00th=[   44],
> >      | 99.00th=[   52], 99.50th=[   59], 99.90th=[   77], 99.95th=[   88],
> >      | 99.99th=[  169]
> >    bw (  KiB/s): min=15664, max=1599456, per=100.00%, avg=897761.07, stdev=504329.17, samples=257
> >    iops        : min= 3916, max=399864, avg=224440.26, stdev=126082.33, samples=257
> >   lat (usec)   : 2=0.01%, 4=0.01%, 10=0.01%, 20=0.01%, 50=98.80%
> >   lat (usec)   : 100=1.18%, 250=0.02%, 500=0.01%
> >   lat (msec)   : 10=0.01%, 2000=0.01%, >=2000=0.01%
> >   cpu          : usr=5.45%, sys=23.92%, ctx=78418, majf=0, minf=14
> >   IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=100.0%, 32=0.0%, >=64=0.0%
> >      submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
> >      complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.1%, 32=0.0%, 64=0.0%, >=64=0.0%
> >      issued rwts: total=0,28889786,0,0 short=0,0,0,0 dropped=0,0,0,0
> >      latency   : target=0, window=0, percentile=100.00%, depth=16
> > 
> > Run status group 0 (all jobs):
> >   WRITE: bw=376MiB/s (394MB/s), 376MiB/s-376MiB/s (394MB/s-394MB/s), io=110GiB (118GB), run=300001-300001msec
> > 
> > Disk stats (read/write):
> >     dm-7: ios=0/22878, merge=0/0, ticks=0/373254, in_queue=373254, util=43.89%, aggrios=0/99746, aggrmerge=0/9246, aggrticks=0/1406831, aggrin_queue=1408420, aggrutil=73.56%
> >   sda: ios=0/99746, merge=0/9246, ticks=0/1406831, in_queue=1408420, util=73.56%
> > 
> > mounted with -o iversion:
> > 
> > $ fio ./4k-write.fio
> > file1: (g=0): rw=write, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=16
> > fio-3.27
> > Starting 1 process
> > Jobs: 1 (f=1): [W(1)][100.0%][eta 00m:00s]                          
> > file1: (groupid=0, jobs=1): err= 0: pid=10369: Wed Jul 20 12:33:57 2022
> >   write: IOPS=96.2k, BW=376MiB/s (394MB/s)(110GiB/300001msec); 0 zone resets
> >     slat (nsec): min=1112, max=1861.5k, avg=1994.58, stdev=890.78
> >     clat (nsec): min=1392, max=2113.3M, avg=156252.71, stdev=15409487.99
> >      lat (usec): min=3, max=2113.3k, avg=158.30, stdev=15409.49
> >     clat percentiles (usec):
> >      |  1.00th=[   37],  5.00th=[   38], 10.00th=[   38], 20.00th=[   38],
> >      | 30.00th=[   39], 40.00th=[   39], 50.00th=[   40], 60.00th=[   40],
> >      | 70.00th=[   41], 80.00th=[   42], 90.00th=[   43], 95.00th=[   45],
> >      | 99.00th=[   53], 99.50th=[   60], 99.90th=[   79], 99.95th=[   90],
> >      | 99.99th=[  174]
> >    bw (  KiB/s): min=  304, max=1540000, per=100.00%, avg=870727.42, stdev=499371.78, samples=265
> >    iops        : min=   76, max=385000, avg=217681.82, stdev=124842.94, samples=265
> >   lat (usec)   : 2=0.01%, 4=0.01%, 10=0.01%, 20=0.01%, 50=98.49%
> >   lat (usec)   : 100=1.48%, 250=0.02%, 500=0.01%
> >   lat (msec)   : 2=0.01%, 2000=0.01%, >=2000=0.01%
> >   cpu          : usr=5.71%, sys=24.49%, ctx=52874, majf=0, minf=18
> >   IO depths    : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=100.0%, 32=0.0%, >=64=0.0%
> >      submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
> >      complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.1%, 32=0.0%, 64=0.0%, >=64=0.0%
> >      issued rwts: total=0,28856695,0,0 short=0,0,0,0 dropped=0,0,0,0
> >      latency   : target=0, window=0, percentile=100.00%, depth=16
> > 
> > Run status group 0 (all jobs):
> >   WRITE: bw=376MiB/s (394MB/s), 376MiB/s-376MiB/s (394MB/s-394MB/s), io=110GiB (118GB), run=300001-300001msec
> > 
> > Disk stats (read/write):
> >     dm-7: ios=1/16758, merge=0/0, ticks=2/341817, in_queue=341819, util=47.93%, aggrios=1/98153, aggrmerge=0/5691, aggrticks=2/1399496, aggrin_queue=1400893, aggrutil=73.42%
> >   sda: ios=1/98153, merge=0/5691, ticks=2/1399496, in_queue=1400893, util=73.42%
> > 
> > -- 
> > Jeff Layton <jlayton@...nel.org>
> > 
> 

-- 
Jeff Layton <jlayton@...nel.org>

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