Re: Re: Next steps with pv_ops for Xen

[Mark Williamson <mark.williamson@cl.cam.ac.uk>]

> Hi Mark,
>
> > Maybe a change to the gntdev userspace API to allow batching
> > of mapping requests?
>
> Something along the lines of the following?

Just like that :-D

When you said "multiple syscalls per mapping" I assumed you meant that we'd 
lose the batching you get by doing a mulicall.  If it's just a couple of 
syscalls (plus, presumably a couple of hypercalls) per batch of mappings, my 
gut says it's probably not going to hurt block performance.  My guts have 
been wrong in (many!) ways before of course...

I guess the overhead *could* be reduced even more by just having a magic ioctl 
that did all the mmap-ing stuff in one operation, but that'd probably be 
really gross if it wasn't necessary!  And I doubt it'd make upstream very 
happy...

We'll also be eliminating the overheads involved in having a blktap ring for 
talking to userspace and having to move requests between that ring and the 
real block ring, so there's some definite wins in overheads as well.

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!