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

Sasha Levin
2011-06-04T10:14:07Z

On Sat, 2011-06-04 at 11:38 +0200, Ingo Molnar wrote:
> * Sasha Levin <levinsasha928@gmail.com> wrote:
>
> > Coalescing MMIO allows us to avoid an exit every time we have a
> > MMIO write, instead - MMIO writes are coalesced in a ring which
> > can be flushed once an exit for a different reason is needed.
> > A MMIO exit is also trigged once the ring is full.
> >
> > Coalesce all MMIO regions registered in the MMIO mapper.
> > Add a coalescing handler under kvm_cpu.
>
> Does this have any effect on latency? I.e. does the guest side
> guarantee that the pending queue will be flushed after a group of
> updates have been done?

Theres nothing that detects groups of MMIO writes, but the ring size is
a bit less than PAGE_SIZE (half of it is overhead - rest is data) and
we'll exit once the ring is full.

--

Sasha.