On Fri, May 01, 2009 at 09:52:18AM -0400, Christoph Lameter wrote:

On Fri, 1 May 2009, Sam Ravnborg wrote:

quoted

Are there any specific reason why we do not support read_mostly on all
architectures?

Not that I know of.

quoted

read_mostly is about grouping rarely written data together
so what is needed is to introduce this section in the remaining
archtectures.

Christoph - git log says you did the inital implmentation.
Do you agree?

Yes.

There is some concern that __read_mostly is needlessly applied to
numerous variables that are not used in hot code paths. This may make
__read_mostly ineffective and actually increase the cache footprint of a
function since global variables are no longer in the same cacheline. If
such a function is called and the caches are cold then two cacheline
fetches have to be done instead of one.

FWIW I think that's a valid concern. Also, I think one can question the
value of __read_mostly for write-through caches, given the mentioned
concern it probably makes things worse for those. IMO there should be
a way to turn it off for arch's that know it's no good for them.

Cheers