Re: [RFC PATCH 00/17] virtual-bus

[Avi Kivity]

Gregory Haskins wrote:

 

> > virtio is already non-kvm-specific (lguest uses it) and
> > non-pci-specific (s390 uses it).
> >     
>
> Ok, then to be more specific, I need it to be more generic than it
> already is.  For instance, I need it to be able to integrate with
> shm_signals.  

Why?

 

> > If you have a good exit mitigation scheme you can cut exits by a
> > factor of 100; so the userspace exit costs are cut by the same
> > factor.  If you have good copyless networking APIs you can cut the
> > cost of copies to zero (well, to the cost of get_user_pages_fast(),
> > but a kernel solution needs that too).
> >     
>
> "exit mitigation' schemes are for bandwidth, not latency.  For latency
> it all comes down to how fast you can signal in both directions.  If
> someone is going to do a stand-alone request-reply, its generally always
> going to be at least one hypercall and one rx-interrupt.  So your speed
> will be governed by your signal path, not your buffer bandwidth.
>   

The userspace path is longer by 2 microseconds (for two additional 
heavyweight exits) and a few syscalls.  I don't think that's worthy of 
putting all the code in the kernel.

--
error compiling committee.c: too many arguments to function

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