Re: More prefetch fall-out

[Eric Dumazet <eric.dumazet@gmail.com>]

Le dimanche 22 mai 2011 à 10:49 -0700, Linus Torvalds a écrit :

> However, one of the breakages is <linux/skbuff.h> that does its own
> list-walking functions ("skb_queue_walk*"), and they do prefetching.
> So now I have the option to either just add <linux/prefetch.h> to that
> file, or remove the prefetches. And you're the one that said that the
> prefetches in the networking code were annoying.
> 
> So should the skb queues use prefetching? I have a hard time judging.
> Are those lists usually long? Is the loop usually large enough that
> there is any point to prefetching the next entry?
> 

Taking a look at various skb_queue_walk* call sites, I think prefetches
are not a clear win, I would just remove them all from skbuff.h

BTW, the skb_queue_walk_safe(), skb_queue_walk_from_safe(),
skb_queue_reverse_walk_safe, skb_queue_reverse_walk_from_safe() dont
have prefetch() calls.