Re: [Xen-devel] PV drivers for HVM guests

["Andrew D. Ball" <aball@xxxxxxxxxx>]

Agreed.  What I meant is that it would be nice if the device model
were modified to have better performance for things like OS/2, where
writing paravirtual drivers would be less emphasized.

Peace.
Andrew

Ky Srinivasan wrote:
> Andrew,
>
> The I/O performance of HVM guests with PV drivers is SIGNIFICANTLY better than 
> what we get without PV drivers. I will post the patches after some additional 
> testing and code cleanup.
>
> Regards,
>
> K. Y
>
>
> > > > On Tue, Oct 3, 2006 at  6:19 PM, in message
> <1159913996.27206.37.camel@localhost>, "Andrew D. Ball" <aball@xxxxxxxxxx>
> wrote: 
>
> > Interesting!  Ideally, there would be better performance in the base HVM
> > device model.  I think I know of some people that are working hard on
> > that.
> >
> > I'm curious to see what you've done for (1) and (2).
> >
> > Peace.
> > Andrew
> >
> > On Tue, 2006-  10-  03 at 16:31 -  0400, Ky Srinivasan wrote:
> >
> > > I am trying to build PV drivers for SLES9 HVM guests. SLES 9 is based on the 
> > 2.6.5 kernel. Since the PV driver code is really designed for the latest 
> > kernel release, I have had many issues/problems in building the PV drivers 
> > for older Linux OS targets -   I have only been looking at the issues with 2.6.5 
> > kernel base and I suspect the problem will be even worse if one were to look 
> > at older Linux kernels. This is unfortunate since PV drivers are so critical 
> > for HVM guests and there is considerable interest in supporting legacy Linux 
> > environments as HVM guests. The problems I have had to deal with can be 
> > broadly classified into:
> > > a) Compiler related issues
> > > b) Missing functionality in the legacy kernel -   this includes features as 
> > well as changed data structures
> >
> > > c) Implementation differences of a given feature
> > >
> > > These differences can be dealt with in a couple of different ways:
> > > 1) Modify the code in the PV drivers under appropriate compilation switches 
> > to deal with the differences in the base kernels.
> >
> > > 2)  Introduce  a compatibility component that bridges the gap between the 
> > current PV code and a given Linux target and leave much of the PV driver  
> > code untouched.
> > > I have implemented both these schemes for the sles9 kernel and would like to 
> > get your input on your preference. I personally like option 2. Going forward, 
> > the evolution of PV drivers needs to be constrained by the required support 
> > for legacy Linux environments. 
> >
> > > Regards,
> > >
> > > K. Y. Srinivasan 
> > >
> > >
> > >
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