From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH 3/7] [I/OAT] Don't offload copies for loopback traffic
Date: Fri, 18 Aug 2006 14:23:39 -0700 (PDT)
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From: Andi Kleen <ak@suse.de>
Date: Fri, 18 Aug 2006 20:17:18 +0200

> 
> > @@ -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.