Re: SMP/DRBVD issues ...

[Avi Kivity <avi@redhat.com>]

On 12/06/2009 01:28 PM, Gareth Bult wrote:
> Hi,
>
> Specific example of SMP slowdowns;
>
> Two hosts (A), (B) running Ubuntu 9.10.
> One guest on (B) running Ubuntu 9.10 on two cores.
>
> VPN connection (OpenVPN) between host (A) and Guest.
> Copy file over VPN from host (A) to Guest over VPN.
>
> Copy seems slow.
>
> Guest CPU usage is around 25% using "top" inside guest.
> Host A usage is minimal (5-10%).
> Host B CPU usage is around 160%.
>
> I'm expecting Host (B) usage to be ~ 30% ish - this is a huge discrepancy.
>
> I'm also noticing during lots of disk/network IO (virtio driver) whereas client / VM load averages tend to be up around the 1.0 mark, looking at the host the load average is showing 10+. (not a specific problem, but curious and concerning)
>
> In real terms, if I do a raw copy (not via the VPN, so it's all IO and no CPU) the copy (scp) runs through at around 40Mb/sec. Via the VPN, I'm getting ~ 6Mb/sec. If I reduce the VM to 1 core, I get 12Mb/sec .. so doubling the cores on the VM halves the speed!
>
>    

Is the time reported on the host user time or system time?

Please post a kvm_stat report when the slowdown occurs.

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