Re: [Xen-users] Release 0.8.9 of GPL PV drivers for Windows

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Mon, May 05, 2008 at 08:32:46PM -0400, jim burns wrote:

> - dom0 vs. domu: obviously, the standard to match is dom0 performance. (I 
> suspect, tho', that non-xen kernel performance would be even better.) Looking 
> at the 4k pattern numbers above, hvm severely lags dom0. Interestingly 
> enough, for the 32k pattern, hvm is doing better than dom0.
>

domU doing better than dom0 usually happens when you use file backed disks on
dom0.. then the memory cache of dom0 will affect the domU results. 
 
> > Could you try iometer on dom0 to see what kind of performance you get
> > there.. or on linux pv domU?
> 
> As you can see above, I did do dom0. I could do a linux pv, but your next 
> idea 
> interests me more.
> 

OK. I think measuring pv domU is worth trying too :)

> > And one more thing.. was your XP HVM single vcpu or more? Did you try
> > binding both dom0 and hvm domU to their own dedicated cpu cores?
> 
> It was vcpu=2.
> 

I think you should re-test with vcpu=1. 

Configure dom0 for 1 vcpu and domU for 1 vcpu and pin the domains to have a 
dedicated core. This way you're not sharing any pcpu's between the domains.
I think this is the "recommended" setup from xen developers for getting
maximum performance. 

I think the performance will be worse when you have more vcpus in use than
your actual pcpu count.. 

> 
> Yeeaaahh - everything tanked! MB/s down, Cpu % up, etc. Console was still a 
> little sluggish. (I suppose pinning cpus might work better with more than one 
> socket on the mobo.) I won't be trying that config again ;-)
> 

Hmm.. interesting. Maybe it was because of the shared pcpu's.. 

-- Pasi


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