Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755178Ab2JGXqA (ORCPT ); Sun, 7 Oct 2012 19:46:00 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:38204 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752964Ab2JGXWG (ORCPT ); Sun, 7 Oct 2012 19:22:06 -0400 Message-Id: <20121007225848.831983606@decadent.org.uk> User-Agent: quilt/0.60-1 Date: Mon, 08 Oct 2012 00:00:16 +0100 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Ed Cashin , "David S. Miller" Subject: [ 102/108] net: do not disable sg for packets requiring no checksum In-Reply-To: <20121007225834.673681075@decadent.org.uk> X-SA-Exim-Connect-IP: 2001:470:1f08:1539:21c:bfff:fe03:f805 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2837 Lines: 73 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ed Cashin [ Upstream commit c0d680e577ff171e7b37dbdb1b1bf5451e851f04 ] A change in a series of VLAN-related changes appears to have inadvertently disabled the use of the scatter gather feature of network cards for transmission of non-IP ethernet protocols like ATA over Ethernet (AoE). Below is a reference to the commit that introduces a "harmonize_features" function that turns off scatter gather when the NIC does not support hardware checksumming for the ethernet protocol of an sk buff. commit f01a5236bd4b140198fbcc550f085e8361fd73fa Author: Jesse Gross Date: Sun Jan 9 06:23:31 2011 +0000 net offloading: Generalize netif_get_vlan_features(). The can_checksum_protocol function is not equipped to consider a protocol that does not require checksumming. Calling it for a protocol that requires no checksum is inappropriate. The patch below has harmonize_features call can_checksum_protocol when the protocol needs a checksum, so that the network layer is not forced to perform unnecessary skb linearization on the transmission of AoE packets. Unnecessary linearization results in decreased performance and increased memory pressure, as reported here: http://www.spinics.net/lists/linux-mm/msg15184.html The problem has probably not been widely experienced yet, because only recently has the kernel.org-distributed aoe driver acquired the ability to use payloads of over a page in size, with the patchset recently included in the mm tree: https://lkml.org/lkml/2012/8/28/140 The coraid.com-distributed aoe driver already could use payloads of greater than a page in size, but its users generally do not use the newest kernels. Signed-off-by: Ed Cashin Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings --- net/core/dev.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/core/dev.c b/net/core/dev.c index a4a0c5a..6cecd40 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -2108,7 +2108,8 @@ static bool can_checksum_protocol(unsigned long features, __be16 protocol) static u32 harmonize_features(struct sk_buff *skb, __be16 protocol, u32 features) { - if (!can_checksum_protocol(features, protocol)) { + if (skb->ip_summed != CHECKSUM_NONE && + !can_checksum_protocol(features, protocol)) { features &= ~NETIF_F_ALL_CSUM; features &= ~NETIF_F_SG; } else if (illegal_highdma(skb->dev, skb)) { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/