Re: [PATCH 2/2] Provide fast path for "rep ins" emulation if possible.

[Gleb Natapov <gleb@redhat.com>]

On Tue, Jun 05, 2012 at 07:27:40PM +0200, Alexander Graf wrote:
> 
> On 24.05.2012, at 12:54, Roedel, Joerg wrote:
> 
> > On Thu, May 24, 2012 at 01:36:51PM +0300, Avi Kivity wrote:
> >> On 05/24/2012 01:34 PM, Roedel, Joerg wrote:
> >>> On Wed, May 23, 2012 at 05:49:31PM +0300, Avi Kivity wrote:
> >>>> On 05/23/2012 05:40 PM, Avi Kivity wrote:
> >>>>> On 05/23/2012 05:08 PM, Gleb Natapov wrote:
> >>>>> If decode assists are not available, we still need to emulate, see 15.33.5.
> >>>>> 
> >>>> 
> >>>> Joerg, the 2010 version of the manual says that the effective segment
> >>>> (10:12) is only available with decode assists.  The 2012 version says
> >>>> it's unconditional. What's correct?
> >>> 
> >>> It is still conditional and only available with decode-assists. I will
> >>> talk to the APM authors to clarify this in the documentation.
> >> 
> >> Thanks.  As it happens it doesn't matter for INS emulation, only OUTS,
> >> unless other bits in that word also depend on decode assists.
> > 
> > Doesn't look like it. All other bits EXITINFO1 bits for the IOIO
> > intercept are documented from the very ancient beginnings of SVM. So the
> > segment number is the only addition.
> 
> I do remember some bits missing in early implementations though. Don't ask me what, I just remember that when looking at intercept logs back in the day, some bits were not set even though they were documented as such - and those were pretty crucial bits, which is why we go through the emulator usually.
> 
I know exactly why code goes through the emulation because I made it do so :)
And the reason was because the previous code didn't handle anything
except string pio to memory with address increment. i.e the case this
patch turns to fast path.

--
			Gleb.