[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] My turn to rant about types... bitops

Always the job of the maintainer to ask why :)
Well, since linux bitops use unsigned long, being the largest machine word and therefore the most efficient, we get alignment issues.

The next request is really the jist of what we are after, doing 64bit operations 32bit aligned data kills us performance wise and WRT bitops cannot be used for atomic ops. If htis was just Xen I'd consider adding 32bit bitops but I doubt I'd be able to do that in Linux which does not provide "u32" bitops.

IIRC assuring this alignement would even help x86, no?

On Oct 5, 2005, at 2:17 PM, Keir Fraser wrote:

On 5 Oct 2005, at 17:52, Jimi Xenidis wrote:

I think around linux-2.4.19 (and thanks to rusty?) bitops.h went s/ void */unsigned long */, any chance is Xen following suit? The next request would be to change all arrays destined for bitops to be defined using unsigned long.

Just cast to 'unsigned long *' when you use those ops. Why work around details of the way that Linux happens to do atomic ops in our interfaces?

 -- Keir

"I got an idea, an idea so smart my head would explode if I even
began to know what I was talking about." -- Peter Griffin (Family Guy)

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.