On 20 May 2011 00:34, Ingo Molnar <mingo@xxxxxxx> wrote: > * David Miller <davem@xxxxxxxxxxxxx> wrote: > >> So, to reiterate, I think you should kill all the list handling >> prefetches off. > > Agreed. > >> What we can do is say "for this specific list use, prefetch does >> in fact help". And provide an interface for that. I imagine there >> are things like inode dirty writeback or some dcache stuff that >> walks large lists and for which prefetch might be appropriate. > > I think the best 'interface' for that is to open-code the prefetch() > right into the loop. This way it becomes well documented and very > visible as well. I talked to some of the CPU people in ARM and, while there are a variety of ARM implementations, for many of them prefetch(0) would result in a TLB miss and go for an expensive page table walk. For mostly 1-element lists like hash table look-up it's not worth having the prefetch (could make it worse). Prefetch is indeed useful for traversing longer lists (and probably more work inside the loop) but I guess we can code the prefetch() explicitly as Dave and Ingo suggested. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
