Re: [RFC PATCH kernel] vfio-pci: Allow write combining

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2017-11-30 at 15:20 +1100, David Gibson wrote:
> > > > This isn't at the top of my priority list to figure out the solution,
> > > > so whoever implements it will need to provide justification as they
> > > > move down the list from more to less preferred solutions.  Thanks,  
> > > 
> > > I am trying... I was really counting on you guys having this discussed in
> > > Prague :(
> > 
> > Should have been there to push your agenda...  Thanks,
> 
> We discussed it briefly, BenH seemed to think there wasn't a big
> difficulty, IIRC, which is why we didn't spend much time on this
> (compared to the other issues).  So, talk to him.

Well, first we established that this wasn't an issue for KVM, so the
importance/urgency went down. It's still useful for DPDK.

Then we discussed quickly the various options, none of them is
particularily *difficult* as in the implementation is rather trivial,
the question is to chose which interface to provide userspace.

I don't have a strong opinion there. The mm guys might object to
hijacking MAP_NONBLOCK, otherwise that seems like the best approach, so
we should run that past them.

Cheers,
Ben.