Am Montag 08 Dezember 2008 schrieb Martin Steigerwald:
> Hi!
>
> I got curious about the recent discussions about the write barrier
> feature[1][2].
>
> Thus I did my own benchmark this evening. Since I use XFS and tested
> with XFS for now only. Write barrier + write cache, no barrier + write
> cache, no write barrier + no write cache. I just did tar -xf
> linux-2.6.27.tar.bz2 and rm -rf linux-2.6.27.
I disabled write cache and barriers for my XFS filesystems on my TP 42
shambhala. During that I did further tests. This time I also include IO
scheduler settings. They are default and have been the same during my
previous tests.
Write cache has about 13 seconds benefit on the barrier enabled XFS for
the tar -xf linux-2.6.27.tar.bz2 workload but no benefit at all for the
rm -rf linux-2.6.27 workload!
And again nobarrier and no cache wins.
On a heavily used /home-XFS - I know it should have more free space:
martin@shambhala:~ -> LANG=C df -hT /home/
Filesystem Type Size Used Avail Use% Mounted on
/dev/sda5 xfs 112G 107G 5.1G 96% /home
It has been grown two times - since 6 AGs instead of the default of 4:
shambhala:~> xfs_info /home
meta-data=/dev/sda5 isize=256 agcount=6, agsize=4883256
blks
= sectsz=512 attr=2
data = bsize=4096 blocks=29299536, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096
log =internal bsize=4096 blocks=32768, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
IO scheduler settings:
martin@shambhala:~> cat /sys/block/sda/queue/scheduler
noop anticipatory deadline [cfq]
martin@shambhala:~> grep "" /sys/block/sda/queue/iosched/*
/sys/block/sda/queue/iosched/back_seek_max:16384
/sys/block/sda/queue/iosched/back_seek_penalty:2
/sys/block/sda/queue/iosched/fifo_expire_async:250
/sys/block/sda/queue/iosched/fifo_expire_sync:123
/sys/block/sda/queue/iosched/quantum:4
/sys/block/sda/queue/iosched/slice_async:40
/sys/block/sda/queue/iosched/slice_async_rq:2
/sys/block/sda/queue/iosched/slice_idle:6
/sys/block/sda/queue/iosched/slice_sync:100
Write barriers and no write cache:
shambhala:~> hdparm -W /dev/sda
/dev/sda:
write-caching = 0 (off)
shambhala:> cat /proc/mounts | egrep "(/ |home)"
rootfs / rootfs rw 0 0
/dev/disk/by-uuid/7fcd9766-bf1a-426a-8a07-2c3e0c510898 / xfs
rw,relatime,attr2,noquota 0 0
/dev/sda5 /home xfs rw,relatime,attr2,logbufs=8,logbsize=256k,noquota 0 0
martin@shambhala:~/Zeit> sync; time tar -xf
~/Linux/Kernel/Mainline/linux-2.6.27.tar.bz2 ; time sync
tar -xf ~/Linux/Kernel/Mainline/linux-2.6.27.tar.bz2 36,71s user 4,22s
system 36% cpu 1:51,58 total
sync 0,00s user 0,05s system 0% cpu 12,689 total
martin@shambhala:~/Zeit> sync; time rm -rf linux-2.6.27 ; time sync
rm -rf linux-2.6.27 0,06s user 3,90s system 17% cpu 22,906 total
sync 0,00s user 0,01s system 6% cpu 0,103 total
Write barriers and write cache:
shambhala:~> hdparm -W1 /dev/sda
/dev/sda:
setting drive write-caching to 1 (on)
write-caching = 1 (on)
martin@shambhala:~/Zeit> sync; time tar -xf
~/Linux/Kernel/Mainline/linux-2.6.27.tar.bz2 ; time sync
tar -xf ~/Linux/Kernel/Mainline/linux-2.6.27.tar.bz2 34,38s user 3,91s
system 38% cpu 1:38,84 total
sync 0,00s user 0,04s system 0% cpu 10,493 total
martin@shambhala:~/Zeit> sync; time rm -rf linux-2.6.27 ; time sync
rm -rf linux-2.6.27 0,07s user 3,98s system 17% cpu 23,511 total
sync 0,00s user 0,01s system 5% cpu 0,126 total
No write barriers and no write cache:
shambhala:> vim fstab
shambhala:> mount -o remount /
shambhala:> mount -o remount /home
shambhala:> cat /proc/mounts | egrep "(/ |home)"
rootfs / rootfs rw 0 0
/dev/disk/by-uuid/7fcd9766-bf1a-426a-8a07-2c3e0c510898 / xfs
rw,relatime,attr2,nobarrier,noquota 0 0
/dev/sda5 /home xfs
rw,relatime,attr2,nobarrier,logbufs=8,logbsize=256k,noquota 0 0
martin@shambhala:~/Zeit> sync; time tar -xf
~/Linux/Kernel/Mainline/linux-2.6.27.tar.bz2 ; time sync
tar -xf ~/Linux/Kernel/Mainline/linux-2.6.27.tar.bz2 30,36s user 3,31s
system 48% cpu 1:08,94 total
sync 0,00s user 0,08s system 0% cpu 17,462 total
martin@shambhala:~/Zeit> sync; time rm -rf linux-2.6.27 ; time sync
rm -rf linux-2.6.27 0,07s user 3,87s system 20% cpu 19,172 total
sync 0,00s user 0,01s system 4% cpu 0,142 total
martin@shambhala:~> date
Mo 8. Dez 22:38:06 CET 2008
Ciao,
--
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
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