netdev - More prefetch fall-out

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Date:	Sun, 22 May 2011 10:49:11 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	Network Development <netdev@...r.kernel.org>
Subject: More prefetch fall-out

So it turns out that the architectures that don't define their
prefetch() macros in <asm/processor.h> (and instead depend on
linux/prefetch.h to give them the default ones) are currently broken.

Fine, that's really trivial to fix. And, in fact, I'm now testing on
x86 by having x86 put its prefetch infrastructure in <asm/prefetch.h>
and thus making sure that you *have* to include <linux/prefetch.h> to
get it (rather than get it accidentally just because everything ends
up including <asm/processor.h>).

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?

                         Linus
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