Re: [Qemu-devel] [RFC] Next gen kvm api

[Avi Kivity]

On 02/05/2012 12:58 PM, Gleb Natapov wrote:
> > > > 
> > > Reduced performance is what I mean. Obviously old guests will continue 
> > > working.
> > 
> > I'm not happy about it either.
> > 
> It is not only about old guests either. In RHEL we pretend to not
> support HPET because when some guests detect it they are accessing
> its mmio frequently for certain workloads. For Linux guests we can
> avoid that by using kvmclock. For Windows guests I hope we will have
> enlightenment timers  + RTC, but what about other guests? *BSD? How often
> they access HPET when it is available? We will probably have to move
> HPET into the kernel if we want to make it usable.

If we have to, we'll do it.

> So what is the criteria for device to be emulated in userspace vs kernelspace
> in new API? Never? What about vhost-net then? Only if a device works in MSI
> mode? This may work for HPET case, but looks like artificial limitation
> since the problem with HPET is not interrupt latency, but mmio space
> access. 

The criteria is, if it's absolutely necessary.

> And BTW, what about enlightenment timers for Windows? Are we going to
> implement them in userspace or kernel?

The kernel.
-- 
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