Re: [Xen-devel] Re: Next steps with pv_ops for Xen

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> >> It gets better, though. The same hook is used in the version of blktap
> >> in linux-2.6.18-xen (not, as far as I can see, in the sparse tree for
> >> xen-3.1-testing):
> >
> > Oh, I'm thinking more in the direction of killing blktap altogether in
> > favor of a pure userspace implementation on top of gntdev.
>
> I think this would represent good progress, though I wonder if there
> would be a performance penalty due to performing the mapping and
> unmapping in user-space (multiple syscalls per mapping versus a single
> hypercall).

Maybe a change to the gntdev userspace API to allow batching of mapping 
requests?

I'm not aware of a batched mmap interface, which would seem to be the ideal 
solution; but it should be possible to batch this stuff somehow.  Although it 
seems like some kind of really weird ioctl might be needed :-S to do it 
*without* such a batched interface...

blktap in userspace, if any performance problems can be addressed, would seem 
to be a far nicer way of doing things.  And it's less code to merge 
upstream ;-)

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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