Re: [PATCH RFC 2/4] Add yield hypercall for KVM guests

Avi Kivity
2010-08-02T08:32:35Z

On 07/26/2010 08:19 PM, Jeremy Fitzhardinge wrote:
> On 07/25/2010 11:14 PM, Srivatsa Vaddagiri wrote:
>> Add KVM hypercall for yielding vcpu timeslice.
>
> Can you do a directed yield?
>

A problem with directed yield is figuring out who to yield to. One idea
is to look for a random vcpu that is not running and donate some runtime
to it. In the best case, it's the lock holder and we cause it to start
running. Middle case it's not the lock holder, but we lose enough
runtime to stop running, so at least we don't waste cpu. Worst case we
continue running not having woken the lock holder. Spin again, yield
again hoping to find the right vcpu.

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