Re: [PATCH] arp_queue: serializing unlink + kfree_skb

Herbert Xu
2005-02-04T02:05:41Z

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On Thu, Feb 03, 2005 at 05:23:57PM -0800, David S. Miller wrote:
>
> You're absolutely right. Ok, so we do need to change kfree_skb().
> I believe even with the memory barrier, the atomic_read() optimization
> is still worth it. atomic ops on sparc64 take a minimum of 40 some odd
> cycles on UltraSPARC-III and later, whereas the memory barrier will
> take up a single cycle most of the time.

OK, here is the patch to do that. Let's get rid of kfree_skb_fast
while we're at it since it's no longer used.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Thanks,
--
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Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
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===== include/linux/skbuff.h 1.59 vs edited =====
--- 1.59/include/linux/skbuff.h 2005-01-11 07:23:55 +11:00
+++ edited/include/linux/skbuff.h 2005-02-04 12:46:15 +11:00
@@ -353,15 +353,11 @@
*/
static inline void kfree_skb(struct sk_buff *skb)
{
- if (atomic_read(&skb->users) == 1 || atomic_dec_and_test(&skb->users))
- __kfree_skb(skb);
-}
-
-/* Use this if you didn't touch the skb state [for fast switching] */
-static inline void kfree_skb_fast(struct sk_buff *skb)
-{
- if (atomic_read(&skb->users) == 1 || atomic_dec_and_test(&skb->users))
- kfree_skbmem(skb);
+ if (likely(atomic_read(&skb->users) == 1))
+ smp_rmb();
+ else if (likely(!atomic_dec_and_test(&skb->users)))
+ return;
+ __kfree_skb(skb);
}

/**