Re: IO on guest is 20 times slower than host

Kurt Yoder
2009-03-31T15:16:08Z

>
> On Mar 29, 2009, at 10:29 AM, Avi Kivity wrote:
>
>> Kurt Yoder wrote:

<snip>

>>
>> Can you loading kvm_amd on this host with 'modprobe kvm-amd npt=0'?
>
> So that's most likely the problem for me:
>
> me@host:/etc/nagios/nrpe_directives$ sudo modprobe kvm-amd npt=0
> FATAL: Error inserting kvm_amd (/lib/modules/2.6.27-11-server/kernel/
> arch/x86/kvm/kvm-amd.ko): Operation not supported
> me@host:/etc/nagios/nrpe_directives$ uname -a
> Linux boron 2.6.27-11-server #1 SMP Thu Jan 29 20:13:12 UTC 2009
> x86_64 GNU/Linux
>
>
> It looks like I need to enable SVM in my BIOS. I'll do that and report
> back on the results.

The AMD virtualization option was disabled in my BIOS. Once I enabled it,
all my problems disappeared:

me@guest:~$ sudo hdparm -t /dev/sda

/dev/sda:
Timing buffered disk reads: 846 MB in 3.00 seconds = 281.73 MB/sec
me@guest:~$ sudo dd if=/dev/zero of=/tmp/bigfile count=1000000
1000000+0 records in
1000000+0 records out
512000000 bytes (512 MB) copied, 3.84358 s, 133 MB/s

I do recall seeing a warning at boot about an error loading kvm-amd, but
it was not onscreen for long. It was something like "error loading module
kvm-amd"; looking back now, I see in the syslog "kvm: disabled by bios".
Perhaps a warning about slow IO should be issued/logged on AMD hosts every
time KVM is brought up without the benefit of the kvm-amd kernel module?
Anyway, I'm happy now.

Thanks Avi for your help.