From: Herbert Xu <herbert.xu@redhat.com>
Date: Thu, 11 Sep 2008 11:04:15 +1000
Subject: [net] enable TSO if supported by at least one device
Message-id: 20080911010415.GA17094@gondor.apana.org.au
O-Subject: [RHEL5.3 PATCH] net: Enable TSO if supported by at least one device
Bugzilla: 461866
RH-Acked-by: Mark McLoughlin <markmc@redhat.com>
RH-Acked-by: David Miller <davem@redhat.com>

Hi:

RHEL5.3 BZ 461866

This patch is needed to allow virtio to push TSO traffic from a
RHEL-5 host to its guests even when the physical NIC does not
support TSO.

Accepted by davem for 2.6.28 upstraem.

net: Enable TSO if supported by at least one device

As it stands users of netdev_compute_features (e.g., bridges/bonding)
will only enable TSO if all consituent devices support it.  This
is unnecessarily pessimistic since even on devices that do not
support hardware TSO and SG, emulated TSO still performs to a par
with TSO off.

This patch enables TSO if at least on constituent device supports
it in hardware.

The direct beneficiaries will be virtualisation that uses bridging
since this means that TSO will always be enabled for communication
from the host to the guests.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/net/core/dev.c b/net/core/dev.c
index 489d044..7cb219c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3576,6 +3576,12 @@ int netdev_compute_features(unsigned long all, unsigned long one)
 		one |= NETIF_F_GSO_SOFTWARE;
 	one |= NETIF_F_GSO;
 
+	/*
+	 * If even one device supports a GSO protocol with software fallback,
+	 * enable it for all.
+	 */
+	all |= one & NETIF_F_GSO_SOFTWARE;
+
         /* If even one device supports robust GSO, enable it for all. */
 	if (one & NETIF_F_GSO_ROBUST)
 		all |= NETIF_F_GSO_ROBUST;