Messages in this thread | | | Date | Wed, 9 May 2007 08:49:23 +0200 | From | Jens Axboe <> | Subject | Re: [2.6.22 PATCH 22/26] dm: bio list helpers |
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On Tue, May 08 2007, Andrew Morton wrote: > > static inline void bio_list_init(struct bio_list *bl) > > { > > bl->head = bl->tail = NULL; > > } > > > > +#define bio_list_for_each(bio, bl) \ > > + for (bio = (bl)->head; bio && ({ prefetch(bio->bi_next); 1; }); \ > > + bio = bio->bi_next) > > + > > I have this vague memory from a long time ago that one particular CPU type > wants to go oops when prefetching from an invalid address. > > Maybe that went away for some reason - we'd have hit it again if it was > real.
Besides, manual prefetching is very rarely a win. I dabbled with some benchmarks a few weeks back (with the doubly linked lists), and in most cases it was actually a loss. So I'd vote for just removing the prefetch() above.
-- Jens Axboe
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