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

>>> Jeremy Fitzhardinge <jeremy@xxxxxxxx> 25.10.08 02:01 >>>
>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).
>> Opinions?
>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.

I don't see the difficulty here: Just add two new operations to pv ops.
If it won't get done before we switch to the pv ops kernel (which implies
full functionality in Dom0 and DomU), I'd certainly merge up this and any
other changes we carry along.


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