Re: [PATCH] Add I/O hypercalls for i386 paravirt

Alan Cox
2007-08-22T17:27:52Z

> out is usually a single byte. Shouldn't be very expensive
> to decode. In fact it should be roughly equivalent to your
> hypercall multiplex.

Why is a performance critical path on a paravirt kernel even using I/O
instructions and not paravirtual device drivers ?

It clearly makes sense to virtualise I/O operations if you are doing that
(so you can do posting, triggers and predicted reply handling guest side
to keep the trap rate sane) but I don't see why this situation occurs in
the first place for paravirt.