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Re: [Xen-devel] [Hackathon minutes] PV block improvements

On Sat, 2013-06-22 at 09:11 +0200, Roger Pau Monnà wrote:
> First because grant_copy is done by the hypervisor, while when using
> persistent grants the copy is done by the guest.

This is true and a reasonable concern.

> Also, grant_copy takes
> the grant lock, so when scaling to a large number of domains there's
> going to be contention around this lock.

Does grant copy really take the lock for the duration of the copy,
preventing any other grant ops from the source and/or target domain?

If true then that sounds like an area which is ripe for optimisation!

However I am hopeful that you are mistaken... __acquire_grant_for_copy()
takes the grant lock while it pins the entry into the active grant entry
list and not for the actual duration of the copy (and likewise
__release_grant_for-copy). I hope Jan can confirm this!


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