Re: [PATCH net-next] net: add a prefetch in socket backlog processing

[Joe Perches <joe@perches.com>]

On Tue, 2012-05-01 at 04:07 +0200, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> TCP or UDP stacks have big enough latencies that prefetching next
> pointer is worth it.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> ---
>  net/core/sock.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 836bca6..1a88351 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1700,6 +1700,7 @@ static void __release_sock(struct sock *sk)
>  		do {
>  			struct sk_buff *next = skb->next;
>  
> +			prefetch(next);
>  			WARN_ON_ONCE(skb_dst_is_noref(skb));
>  			skb->next = NULL;
>  			sk_backlog_rcv(sk, skb);

Hi Eric.

Why should next be "prefetch"ed when
two lines below it's set to null and
the only use is as a pointer not as
an apparently undereferenced pointer?