From patchwork Mon Oct 21 12:26:03 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yunsheng Lin X-Patchwork-Id: 1180550 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=none (no SPF record) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=huawei.com Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 46xbXx1wrMz9sPZ for ; Mon, 21 Oct 2019 23:29:05 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728719AbfJUM3D (ORCPT ); Mon, 21 Oct 2019 08:29:03 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:4697 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727985AbfJUM3C (ORCPT ); Mon, 21 Oct 2019 08:29:02 -0400 Received: from DGGEMS413-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 54A23144C352E7C2A96E; Mon, 21 Oct 2019 20:28:58 +0800 (CST) Received: from localhost.localdomain (10.69.192.58) by DGGEMS413-HUB.china.huawei.com (10.3.19.213) with Microsoft SMTP Server id 14.3.439.0; Mon, 21 Oct 2019 20:28:54 +0800 From: Yunsheng Lin To: CC: , , , , , , , Subject: [PATCH RFC] net: vlan: reverse 4 bytes of vlan header when setting initial MTU Date: Mon, 21 Oct 2019 20:26:03 +0800 Message-ID: <1571660763-117936-1-git-send-email-linyunsheng@huawei.com> X-Mailer: git-send-email 2.8.1 MIME-Version: 1.0 X-Originating-IP: [10.69.192.58] X-CFilter-Loop: Reflected Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Currently the MTU of vlan netdevice is set to the same MTU of the lower device, which requires the underlying device to handle it as the comment has indicated: /* need 4 bytes for extra VLAN header info, * hope the underlying device can handle it. */ new_dev->mtu = real_dev->mtu; Currently most of the physical netdevs seems to handle above by reversing 2 * VLAN_HLEN for L2 packet len. But for vlan netdev over vxlan netdev case, the vxlan does not seems to reverse the vlan header for vlan device, which may cause performance degradation because vxlan may emit a packet that exceed the MTU of the physical netdev, and cause the software TSO to happen in ip_finish_output_gso(), software TSO call stack as below: => ftrace_graph_call => tcp_gso_segment => tcp4_gso_segment => inet_gso_segment => skb_mac_gso_segment => skb_udp_tunnel_segment => udp4_ufo_fragment => inet_gso_segment => skb_mac_gso_segment => __skb_gso_segment => __ip_finish_output => ip_output => ip_local_out => iptunnel_xmit => udp_tunnel_xmit_skb => vxlan_xmit_one => vxlan_xmit => dev_hard_start_xmit => __dev_queue_xmit => dev_queue_xmit => vlan_dev_hard_start_xmit => dev_hard_start_xmit => __dev_queue_xmit => dev_queue_xmit => neigh_resolve_output => ip_finish_output2 => __ip_finish_output => ip_output => ip_local_out => __ip_queue_xmit => ip_queue_xmit => __tcp_transmit_skb => tcp_write_xmit => __tcp_push_pending_frames => tcp_push => tcp_sendmsg_locked => tcp_sendmsg => inet_sendmsg => sock_sendmsg => sock_write_iter => new_sync_write => __vfs_write => vfs_write => ksys_write => __arm64_sys_write => el0_svc_common.constprop.0 => el0_svc_handler => el0_svc This patch set initial MTU of the vlan device to the MTU of the lower device minus vlan header to handle the above case. Signed-off-by: Yunsheng Lin --- net/8021q/vlan.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c index 54728d2..0c26b92 100644 --- a/net/8021q/vlan.c +++ b/net/8021q/vlan.c @@ -261,10 +261,9 @@ static int register_vlan_device(struct net_device *real_dev, u16 vlan_id) return -ENOBUFS; dev_net_set(new_dev, net); - /* need 4 bytes for extra VLAN header info, - * hope the underlying device can handle it. - */ - new_dev->mtu = real_dev->mtu; + new_dev->mtu = real_dev->mtu - VLAN_HLEN; + if (new_dev->mtu < ETH_MIN_MTU) + new_dev->mtu = ETH_MIN_MTU; vlan = vlan_dev_priv(new_dev); vlan->vlan_proto = htons(ETH_P_8021Q);