Re: mini-guest io emulation

[Anthony Liguori <aliguori@us.ibm.com>]

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
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