Re: [PATCH] kvm tools: Add MMIO coalescing support

Ingo Molnar
2011-06-04T11:27:48Z

* Alexander Graf <agraf@suse.de> wrote:

> > So? I only inquired about latencies, asking what impact on
> > latencies is. Regardless of the circumstances we do not want to
> > introduce unbound latencies.
> >
> > If there are no unbound latencies then i'm happy.
>
> Sure, I'm just saying that the mechanism was invented for
> unmodified guests :).

Well, but that does not excuse the introduction of unbound latencies.
(if those latencies are introduced here - i don't know, i'm asking.)

> > Well, since user-space gets the MMIOs only once the guest exits
> > it's not independent, is it?
>
> If we don't know when a guest ends an MMIO stream, we can't
> optimize it. Period. [...]

But that's no excuse. If you cannot optimize them without
unnacceptable collateral damage then don't optimize it then.

That's why i asked what the damage is - if there's any damage.

Thanks,

Ingo