Re: [Xen-devel] [RFC PATCH] xen: comment opaque expression in __page_to_virt

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Jan Beulich writes ("Re: [RFC PATCH] xen: comment opaque expression in 
__page_to_virt"):
> No, that's not precise. There's really not much of a win to be had
> on 32-bit (division by 3 and division by 24 (sizeof(struct page_info))
> should be the same in speed.
> 
> The win is on x86-64, where sizeof(struct page_info) is a power
> of 2, and hence the pair of shifts (right, then left) can be reduced
> to a single one.
> 
> Yet (for obvious reasons) the code ought to not break anything
> if even on x86-64 the size of the structure would change, hence
> it needs to be that complex (and can't be broken into separate,
> simpler implementations for 32- and 64-bits).

Thanks.  Do you want to post a revised version of my patch or shall I
do so ?  (If so please confirm that I should put your s-o-b on it for
your wording above.)

Ian.

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