netdev - Re: [RFC] csum experts, csum_replace2() is too expensive

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Message-ID: <1395363257.9114.111.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 20 Mar 2014 17:54:17 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Patrick McHardy <kaber@...sh.net>,
	"H.K. Jerry Chu" <hkchu@...gle.com>,
	Michael Dalton <mwdalton@...gle.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] csum experts, csum_replace2() is too expensive

On Fri, 2014-03-21 at 08:13 +0800, Herbert Xu wrote:

> Your patch makes sense to me.  However does it actually help
> your 1% in the GRO profile?

Well, I caught this strange csum_partial() presence in a profile,
but my question was more general than the GRO use case.

(BTW the patch didn't even compile ;) )

I guess that in GRO case, the following would be even faster...

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 8c54870db792..b8fe5e8a02dd 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1361,6 +1361,7 @@ static struct sk_buff **inet_gro_receive(struct sk_buff **head,
 	if (!ops || !ops->callbacks.gro_receive)
 		goto out_unlock;
 
+	/* GRO is limited to IPv4 with no options : ihl = 5 */
 	if (*(u8 *)iph != 0x45)
 		goto out_unlock;
 
@@ -1434,8 +1435,10 @@ static int inet_gro_complete(struct sk_buff *skb, int nhoff)
 	int proto = iph->protocol;
 	int err = -ENOSYS;
 
-	csum_replace2(&iph->check, iph->tot_len, newlen);
+	/* GRO is limited to IPv4 with no options : ihl = 5 */
 	iph->tot_len = newlen;
+	iph->check = 0;
+	iph->check = ip_fast_csum((u8 *)iph, 5);
 
 	rcu_read_lock();
 	ops = rcu_dereference(inet_offloads[proto]);



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