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xen-devel
Re: [Xen-devel] Re: Next steps with pv_ops for Xen
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dgm36@xxxxxxxxx |
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Subject: |
Re: [Xen-devel] Re: Next steps with pv_ops for Xen |
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From: |
Mark Williamson <mark.williamson@xxxxxxxxxxxx> |
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Date: |
Mon, 3 Dec 2007 19:08:08 +0000 |
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Cc: |
xen-devel@xxxxxxxxxxxxxxxxxxx, 'Eduardo Habkost' <ehabkost@xxxxxxxxxx>, 'Juan Quintela' <quintela@xxxxxxxxxx>, "'Stephen C. Tweedie'" <sct@xxxxxxxxxx>, 'Jan Beulich' <jbeulich@xxxxxxxxxx>, 'Glauber de Oliveira Costa' <gcosta@xxxxxxxxxx>, 'Chris Wright' <chrisw@xxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, 'Gerd Hoffmann' <kraxel@xxxxxxxxxx> |
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Mon, 03 Dec 2007 11:08:49 -0800 |
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> 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!
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