On Tue, 28 Mar 2006, Chen, Kenneth W wrote: > > + /* mmap_sem is performance critical.... */ > > + prefetchw(&mm->mmap_sem); > > + > > I would say push that a couple of lines down after checking !mm > > if (in_atomic() || !mm) > goto no_context; I initially also thought that would be better. > If you insist on prefetching mmap_sem at the very beginning of the > function, then use speculative load, it will "nat" right away with > null pointer without generating any exception at all. It is super > fast because of nat page. I saw David Mosberger's patch from last year http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=458f935527372499b714bf4f8e646a68bb0f52e3 and it seems that he implemented fast handling of these NULL cases? mm == NULL is very rare so I think we can try to prefetch as early as possible. - : send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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