netdev - Re: More prefetch fall-out

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Message-ID: <1306088626.12435.27.camel@edumazet-laptop>
Date:	Sun, 22 May 2011 20:23:46 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: More prefetch fall-out

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.



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