On Fri, May 01, 2009 at 09:52:18AM -0400, Christoph Lameter wrote: > On Fri, 1 May 2009, Sam Ravnborg wrote: > > > Are there any specific reason why we do not support read_mostly on all > > architectures? > > Not that I know of. > > > 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
