[Xen-devel] poor I/O performance on domU

[Jan Kundrát <jan.kundrat@xxxxxx>]

Hi,
comparing disk I/O performance of domain0 running gentoo and 
unprivileged domain with ttylinux (tried multiple times, results differ 
in ~ 1sec range):
In domain0:

zirafa ~ # time dd if=/dev/hda of=/dev/null bs=1M count=500
500+0 records in
500+0 records out

real    0m27.344s
user    0m0.000s
sys     0m2.280s
zirafa ~ # hdparm -t /dev/hda

/dev/hda:
 Timing buffered disk reads:   56 MB in  3.03 seconds =  18.48 MB/sec


-----------------------------
And for unprivileged domains:

root@tiny ~ # time dd if=/dev/sdb1 of=/dev/null bs=1M count=500
500+0 records in
500+0 records out

real    0m41.962s
user    0m0.010s
sys     0m1.920s
root@tiny ~ # hdparm -t /dev/sdb1

/dev/sdb1:
 Timing buffered disk reads:  64 MB in  5.32 seconds = 12.03 MB/sec
ioctl 00001261 not supported by Xen blkdev
hdparm:  BLKFLSBUF: Function not implemented
ioctl 0000031f not supported by Xen blkdev
hdparm: HDIO_DRIVE_CMD: Function not implemented

I've tried exporting /dev/hda as /dev/sdb, /dev/sdb1 and /dev/hda, all 
of them in read-only mode. Results look very similar, only `hdparm -t 
/dev/hda` from domainU complains bit more:
root@tiny ~ # hdparm -t /dev/hda

/dev/hda:
 Timing buffered disk reads:  64 MB in  5.38 seconds = 11.90 MB/sec
ioctl 00001261 not supported by Xen blkdev
hdparm:  BLKFLSBUF: Function not implemented
ioctl 0000031f not supported by Xen blkdev
hdparm: HDIO_DRIVE_CMD: Function not implemented
[XEN:vbd_update:drivers/xen/blkfront/blkfront.c:194] >
[XEN:vbd_update:drivers/xen/blkfront/blkfront.c:195] <

I'm using some older version of Xen/2, compiled on 14 Nov 2004, machine 
is celeron/466 with 256MB of RAM, 64 for dom0.
ttylinux.conf:
kernel = "/boot/vmlinuz-2.6.9-xenU"
memory = 64
name = "ttylinux"
nics = 1
ip = "10.18.6.10"
disk = ['file:/home/storage/ttylinux-xen,sda1,r','phy:hda,hda,r']
root = "/dev/sda1 ro"

ttylinux's rootfs is exported from ext3 fs via loopback device, could it 
be the cause of troubles?
-jkt

--
cd /local/pub && more beer > /dev/mouth



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