Re: [Xen-devel] mini-guest io emulation

[Anthony Liguori <aliguori@xxxxxxxxxx>]

Nakajima, Jun wrote:
> For the "mini guest", I think it could be much easier if we
> substantially strip down xenlinux rather than adding (eventually) a lot
> of stuff to the current mini-os, mainly because we need probably a
> multi-threaded run-time environment, scheduler, memory allocator, event
> handling, drivers such as xenbus/netfront/blkfront, etc. At least, I
> think we can use xenlinux as the development platform. For example,
> implement the qemu-dm as a driver adding the infrastructure required
> (e.g. small in-kernel glibc).
>   
Once you get past vl.c, qemu-dm has very little reliance on glibc 
functions.  Since we're only trying to do hardware emulation here, I'd 
expect that vl.c would not be included.
I suspect stripping down Linux is going to prove harder in the long 
run.  As Jacob mentioned, you only really need a simple page allocator.  
The only reasons I can think of to use threads is XenBus (threads 
shouldn't be required to implement it) and asynchronous IO.
I think an interesting alternative for AIO would actually be to create 
another VCPU specifically for the mini-os code to run in.  The 
physically analogy is sane and if you truly do need more parallelism you 
can always just use two VCPUs.
Regards,

Anthony Liguori
> > Once the above is working we'll be in good shape. We can remove all
> > the skany qemu-dm support from the tools as from their POV paravirt
> > and hvm guests will look identical. It should also be easy to
> > implement save/restore of hvm guests -- just save the miniguest as
> > part of the hvm guests', memory image. The next stage would then be
> > to improve performance by enhancing the device models, e.g. adding a
> > network card that suports jumbo frames and csum offload, and requires
> > fewer vmexits in operation.
> >
> > How best to move forward on this? Any volunteers?
> >
> > Thanks,
> > Ian
> >
> >     
> Jun
> ---
> Intel Open Source Technology Center
>
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