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Re: [Xen-devel] [PATCH, RFC] i386: highmem access assistance hypercalls

Jan Beulich wrote:
While looking at the origin of very frequently executed hypercalls I
realized that the high page accessor functions in Linux would be good
candidates to handle in the hypervisor - clearing or copying to/from
a high page is a pretty frequent operation (provided there's enough
memory in the domain). While prior to the first submission I only
measured kernel builds (where the results are not hinting at a
meaningful improvement), I now found time to do a more specific
analysis: page clearing is being improved by about 20%, page copying
doesn't seem to significantly benefit (though that may be an effect of
the simplistic copy_page() implementation Xen currently uses) -
nevertheless I would think that if one function is supported by the
hypervisor, then the other should also be.

The hypervisor patch is below (using temporary numbers for the newly
added sub-hypercalls), the Linux patch didn't change over the first
submission (if the patch here is acceptable, I'll create a version
that applies to the 2.6.18 tree).


Do you have any thoughts about what it would take to make this be useful in a pvops kernel? If the Novell kernel is the only user, it seems like a bit of a dead end.


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