Re: [Xen-users] Running Xen 2.0 for Counter Strike: Source

[Ernst Bachmann <e.bachmann@xxxxxxxx>]

On Wednesday 15 February 2006 10:37, Bart van den Heuvel wrote:
> I have recompiled the kernels, both dom0 and domU. Counterstrike comes in
> a compiled form (silly enterprises still do that :-)
>
> All is wel and i got the change to compile in the bigmem option! So i'm
> very happy there. I can now use more mem for my virtual servers... But
> thats where the happyness stops!
>
> Instead of a performance upgrade fps is now steady on 1, so the 1000 hz
> options made the fps value go from 50 to 1 instead of a higher value.
>
> I'm running like this for a few hours... Maybe more inspiration will come
> to me.
>
The HZ Value sets how often timer interrups occur, so instead of interrupting 
work 250 times a second, you now interrupt it 1000 times.

I guess timer interrupts in xen are more expensive than on plain linux, since 
they also involve the hypervisor (correct me if I'm wrong here)

if three domains use the same cpu, xen needs to switch the running domain 3000 
times a second, I guess you waste a lot of cycles there.

Another reason (wild guess) could be: the hypervisor still generates 
interrupts at 250HZ, but now the domU kernel now expects them coming at 
1000Hz, hence the internal timing of the kernel is way off, resulting of the 
timing source of your CS server working only on full seconds now => 1 frame 
per second max...

For applications requiring short response time, a "lesser" virtualization 
method, like linux-vserver, might provide much better performance.

/Ernst

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