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

[Jeremy Fitzhardinge <jeremy@goop.org>]

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.

    J