Re: [Xen-devel] unnecessary VCPU migration happens again

[Emmanuel Ackaouy <ack@xxxxxxxxxxxxx>]

On Dec 19, 2006, at 8:02, Xu, Anthony wrote:
> Your patch is good, and reduce the majority of unnecessary migrations.
> But the unnecessary migration still exist. I can still see about 5% 
> performance
> degradation on above benchmark( KB and LTP).
> In fact this patch had helped a lot (from 27% to 5%)
>
> I can understand it is impossible to implement spreading VCPU over all 
> sockets/cores
> and eliminate all unnecessary migration in the same time.
>
> Is it possible for us to add a argument to function scheduler_init to 
> enable/disable
> spreading VCPU feature?
I don't think this is a good idea. If you want to disable migration, 
you can always
pin your VCPUs in place yourself using the cpu affinity masks.

If the attempt to balance work across sockets hurts performance of 
reasonable
benchmarks, then perhaps it's still being too aggressive. right now, 
such a
migration could happen on 10ms boundaries. i can try to smooth this 
further.
Can you dump the credit scheduler stat counter before and after you run 
the
benchmark? (^A^A^A on the dom0/hypervisor console to switch to the 
hypervisor
and then type the "r" key to dump scheduler info). That along with an 
idea of the
elapsed time between the two stat samples would be handy.

Cheers,
Emmanuel.


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