Dor Laor wrote:
On 11/15/2009 02:00 PM, Gordan Bobic wrote:
Dor Laor wrote:
On 11/14/2009 04:23 PM, Gordan Bobic wrote:
I just tried paravirtualized virtio block devices, and my tests show
that they are approximately 30% slower than emulated IDE devices. I'm
guessing this isn't normal. Is this a known issue or am I likely to
have
mosconfigured something? I'm using 64-bit RHEL/CentOS 5 (both host and
guest).
Please try to change the io scheduler on the host to io scheduler, it
should boost your performance back.
I presume you mean the deadline io scheduler. I tried that (kernel
parameter elevator=deadline) and it made no measurable difference
compared to the cfq scheduler.
What version of kvm do you use? Is it rhel5.4?
It's RHEL 5.4.
$ rpm -qa | grep -i kvm
kmod-kvm-83-105.el5_4.9
kvm-83-105.el5_4.9
Can you post the qemu cmdline and the perf test in the guest?
Here is what is in the libvirt log:
For IDE emulation:
LC_ALL=C PATH=/sbin:/usr/sbin:/bin:/usr/bin HOME=/root USER=root
LOGNAME=root /usr/libexec/qemu-kvm -S -M pc -m 2048 -smp 4 -name
RHEL_5_x86-64 -uuid cb44b2c5-e64b-848f-77af-f8e7f02fa2ca
-no-kvm-pit-reinjection -monitor pty -pidfile
/var/run/libvirt/qemu//RHEL_5_x86-64.pid -boot c -drive
file=/var/lib/libvirt/images/RHEL_5_x86-64.img,if=ide,index=0,boot=on
-net nic,macaddr=54:52:00:5a:67:4b,vlan=0,model=e1000 -net
tap,fd=15,script=,vlan=0,ifname=vnet0 -serial pty -parallel none -usb
-vnc 127.0.0.1:0 -k en-gb
For virtio:
LC_ALL=C PATH=/sbin:/usr/sbin:/bin:/usr/bin HOME=/root USER=root
LOGNAME=root /usr/libexec/qemu-kvm -S -M pc -m 2048 -smp 4 -name
RHEL_5_x86-64 -uuid cb44b2c5-e64b-848f-77af-f8e7f02fa2ca
-no-kvm-pit-reinjection -monitor pty -pidfile
/var/run/libvirt/qemu//RHEL_5_x86-64.pid -boot c -drive
file=/var/lib/libvirt/images/CentOS_5_x86-64.img,if=virtio,index=0,boot=on
-net nic,macaddr=54:52:00:5a:67:4b,vlan=0,model=e1000 -net
tap,fd=15,script=,vlan=0,ifname=vnet0 -serial pty -parallel none -usb
-vnc 127.0.0.1:0 -k en-gb
The test is building the Linux kernel (only taking the second run to
give the test the benefit of local cache):
make clean; make -j8 all; make clean; sync; time make -j8 all
This takes about 10 minutes with IDE disk emulation and about 13 minutes
with virtio. I ran the tests multiple time with most non-essential
services on the host switched off (including cron/atd), and the guest in
single-user mode to reduce the "noise" in the test to the minimum, and
the results are pretty consistent, with virtio being about 30% behind.
Lastly, do you use cache=wb on qemu? it's just a fun mode, we use
cache=off only.
I don't see the option being set in the logs, so I'd guess it's whatever
qemu-kvm defaults to.
Gordan
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
