Re: [PATCHv4 3/5] KVM: emulator: move some address manipulation function out of emulator code.

[Gleb Natapov <gleb@redhat.com>]

On Thu, Jul 19, 2012 at 04:34:50PM +0300, Avi Kivity wrote:
> On 07/19/2012 01:49 PM, Gleb Natapov wrote:
> >> All those exports suggest it's better to move the fast path into the
> >> emulator. 
> > 
> > We've already being through that. Putting the code into emulator gives
> > us nothing unless it also works on emulator context and working on
> > partially initialized emulator context is first dangerous and second
> > slower.
> 
> We can make it work on an x86_pio_ctxt.  What it gives us is common
> code. (x86_emulate_ctxt can include a x86_pio_ctxt when it does pio).
> 
My patches do similar thing, but instead of x86_pio_ctxt they use
x86_linearize_ctx. The code is common.

> > 
> >>  Suppose we change register access to use callbacks instead of
> >> bulk load/save, could we reuse the exising code?
> >> 
> > I do not see that problem. This helper function do basic arithmetics
> > on three values. The value itself will be fetched on demand by the emulator.
> 
> I meant to reduce the emulator initialization cost, so it isn't slow.
> 
> btw, I'm guessing that the main speedup comes not from avoiding the
> decode, but by doing page-at-a-time instead of word-at-a-time.
> 
And hacking emulator doing page at a time is not trivial an complicates
it for no good reason. BTW you were the one who suggested implementing
fast pio as a separate code path.

--
			Gleb.