Re: [PATCH RFC 1/2] kvm: Handle undercommitted guest case in PLEhandler

[Raghavendra K T]

On 09/27/2012 02:20 PM, Avi Kivity wrote:
> On 09/25/2012 04:43 PM, Jiannan Ouyang wrote:
> > I've actually implemented this preempted_bitmap idea.
>
> Interesting, please share the code if you can.
>
> > However, I'm doing this to expose this information to the guest, so the
> > guest is able to know if the lock holder is preempted or not before
> > spining. Right now, I'm doing experiment to show that this idea works.
> >
> > I'm wondering what do you guys think of the relationship between the
> > pv_ticketlock approach and PLE handler approach. Are we going to adopt
> > PLE instead of the pv ticketlock, and why?
>
> Right now we're searching for the best solution.  The tradeoffs are more
> or less:
>
> PLE:
> - works for unmodified / non-Linux guests
> - works for all types of spins (e.g. smp_call_function*())
> - utilizes an existing hardware interface (PAUSE instruction) so likely
> more robust compared to a software interface
>
> PV:
> - has more information, so it can perform better

Should we also consider that we always have an edge here for non-PLE
machine?

> Given these tradeoffs, if we can get PLE to work for moderate amounts of
> overcommit then I'll prefer it (even if it slightly underperforms PV).
> If we are unable to make it work well, then we'll have to add PV.
Avi,
Thanks for this summary.. It is of great help to proceed in right
direction..

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