On Tue, 29 Aug 2006, Andi Kleen wrote: > On Tuesday 29 August 2006 17:56, Christoph Lameter wrote: > > On Tue, 29 Aug 2006, David Howells wrote: > > > > > Because i386 (and x86_64) can do better by using XADDL/XADDQ. > > > > And Ia64 would like to use fetchadd.... > > This might be a dumb question, but I would expect even on altix > with lots of parallel faulting threads rwsem performance be basically > limited by aquiring the cache line and releasing it later to another CPU.
Correct. However, a cmpxchg may have to acquire that cacheline multiple times in a highly contented situation. A fetchadd acquires the cacheline only once. > Do you really think it will make much difference what particular atomic > operation is used? The basic cost of sending the cache line over the > interconnect should be all the same, no? And once the cache line is local > it should be reasonably fast either way. We have long tuned that portion of the code and therefore we are skeptical of changes. But if we cannot measure a difference to a generic implemenentation then it would be okay. - To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
