Re: Xen is a feature

[Avi Kivity]

Ingo Molnar wrote:
> * Avi Kivity <avi@xxxxxxxxxx> wrote:
>
>   
> > Ingo Molnar wrote:
> >     
> > > > There is in fact a way to get dom0 support with nearly no changes to 
> > > > Linux, but it involves massive changes to Xen itself and requires 
> > > > hardware support: run dom0 as a fully virtualized guest, and assign 
> > > > it all the resources dom0 can access.  It's probably a massive effort 
> > > > though.
> > > >
> > > > I've considered it for kvm when faced with the "I want a thin  
> > > > hypervisor" question: compile the hypervisor kernel with PCI support 
> > > > but nothing else (no CONFIG_BLOCK or CONFIG_NET, no device drivers), 
> > > > load userspace from initramfs, and assign host devices to one or more 
> > > > privileged guests.  You could probably run the host with a heavily 
> > > > stripped configuration, and enjoy the slimness while every interrupt 
> > > > invokes the scheduler, a context switch, and maybe an IPI for good 
> > > > measure.
> > > >     
> > > >         
> > > This would be an acceptable model i suspect, if someone wants a 'slim 
> > > hypervisor'.
> > >
> > > We can context switch way faster than we handle IRQs. Plus in a  
> > > slimmed-down config we could intentionally slim down aspects of the  
> > > scheduler as well, if it ever became a measurable performance issue.  
> > > The hypervisor would run a minimal user-space and most of the  
> > > context-switching overhead relates to having a full-fledged user-space 
> > > with rich requirements. So there's no real conceptual friction between 
> > > a 'lean and mean' hypervisor and a full-featured native kernel.
> > >   
> > >       
> > The context switch would be taken by the Xen scheduler, not the Linux  
> > scheduler. [...]
> >     
>
> The 'slim hypervisor' model i was suggesting was a slimmed down 
> _Linux_ kernel.
>   

Yeah, I lost the context.  I should reduce my own context switching.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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