netdev - Re: using software TSO on non-TSO capable netdevices

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Message-ID: <20080731094536.GC23814@xi.wantstofly.org>
Date:	Thu, 31 Jul 2008 11:45:36 +0200
From:	Lennert Buytenhek <buytenh@...tstofly.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	akarkare@...vell.com, nico@....org
Subject: Re: using software TSO on non-TSO capable netdevices

On Thu, Jul 31, 2008 at 11:54:10AM +0800, Herbert Xu wrote:

> > +	return (caps & NETIF_F_SG) &&
> > +		 (((type == SKB_GSO_TCPV4 || type == SKB_GSO_UDP) &&
> 
> Nobody has written software UFO yet.  Let's just stick TCP for
> now.

OK, how about:



From: Lennert Buytenhek <buytenh@...tstofly.org>
Subject: [NET] use software GSO for SG+CSUM capable netdevices

If a netdevice does not support hardware GSO, allowing the stack to
use GSO anyway and then splitting the GSO skb into MSS-sized pieces
as it is handed to the netdevice for transmitting is likely still
a win at least as far as CPU usage is concerned, since it reduces
the number of trips through the output path.

This patch enables the use of GSO on any netdevice that supports SG
and hardware checksumming.  If a GSO skb is then sent to a netdevice
that supports SG and checksumming but does not support hardware GSO,
net/core/dev.c:dev_hard_start_xmit() will take care of doing the
necessary GSO segmentation in software.

Signed-off-by: Lennert Buytenhek <buytenh@...vell.com>

Index: linux-2.6.27-rc1/include/net/sock.h
===================================================================
--- linux-2.6.27-rc1.orig/include/net/sock.h
+++ linux-2.6.27-rc1/include/net/sock.h
@@ -1085,7 +1085,12 @@ extern struct dst_entry *sk_dst_check(st
 
 static inline int sk_can_gso(const struct sock *sk)
 {
-	return net_gso_ok(sk->sk_route_caps, sk->sk_gso_type);
+	int caps = sk->sk_route_caps;
+	int type = sk->sk_gso_type;
+
+	return (caps & NETIF_F_SG) &&
+		 ((type == SKB_GSO_TCPV4 && (caps & NETIF_F_V4_CSUM)) ||
+		  (type == SKB_GSO_TCPV6 && (caps & NETIF_F_V6_CSUM)));
 }
 
 extern void sk_setup_caps(struct sock *sk, struct dst_entry *dst);
--
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