Re: [PATCH 3/7] [I/OAT] Don't offload copies for loopback traffic

From: Andi Kleen <redacted>
Date: Fri, 18 Aug 2006 20:17:18 +0200

quoted

@@ -1136,7 +1137,8 @@ int tcp_recvmsg(struct kiocb *iocb, stru
 	skb = skb_peek_tail(&sk->sk_receive_queue);
 	if (skb)
 		available = TCP_SKB_CB(skb)->seq + skb->len - (*seq);
-	if ((available < target) &&
+	dst = __sk_dst_get(sk);
+	if ((available < target) && (!dst || (dst->dev != &loopback_dev)) &&

You just added another potential cache miss to a critical
path. A bit flag in the socket would be better.

But is it really worth this ugly special case?

I think it isn't.  It is really gross.