Re: [PATCH] kvm-vmx: add module parameter to avoid trapping HLT instructions (v2)

Anthony Liguori
2010-12-03T03:21:28Z

On 12/02/2010 08:42 PM, Chris Wright wrote:
> OK, let's say a single PCPU == 12 Compute Units.
>
> If the guest is the first to migrate to a newly added unused host, and
> we are using either non-trapping hlt or Marcelo's non-yielding trapping
> hlt, then that guest is going to get more CPU than it expected unless
> there is some throttling mechanism. Specifically, it will get 12CU
> instead of 1-3CU.
>
> Do you agree with that?
>

Yes.

There's definitely a use-case to have a hard cap.

But I think another common use-case is really just performance
isolation. If over the course of a day, you go from 12CU, to 6CU, to
4CU, that might not be that bad of a thing.

If the environment is designed correctly, of N nodes, N-1 will always be
at capacity so it's really just a single node hat is under utilized.

Regards,

Anthony Liguori

> thanks,
> -chris
>