From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: RE: [net] e1000: Small packets may get corrupted during padding by HW Date: Mon, 17 Sep 2012 09:58:22 +0200 Message-ID: <1347868702.26523.79.camel@edumazet-glaptop> References: <1347740217-10257-1-git-send-email-jeffrey.t.kirsher@intel.com> <061C8A8601E8EE4CA8D8FD6990CEA89130DC20AA@ORSMSX102.amr.corp.intel.com> <50552FF1.5030708@intel.com> <061C8A8601E8EE4CA8D8FD6990CEA89130DC3631@ORSMSX102.amr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: "Fastabend, John R" , Michal Miroslaw , "Kirsher, Jeffrey T" , "davem@davemloft.net" , "netdev@vger.kernel.org" , "gospo@redhat.com" , "sassmann@redhat.com" To: "Dave, Tushar N" Return-path: Received: from mail-bk0-f46.google.com ([209.85.214.46]:51166 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754066Ab2IQH62 (ORCPT ); Mon, 17 Sep 2012 03:58:28 -0400 Received: by bkwj10 with SMTP id j10so2304930bkw.19 for ; Mon, 17 Sep 2012 00:58:27 -0700 (PDT) In-Reply-To: <061C8A8601E8EE4CA8D8FD6990CEA89130DC3631@ORSMSX102.amr.corp.intel.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 2012-09-17 at 07:33 +0000, Dave, Tushar N wrote: > >-----Original Message----- > >From: netdev-owner@vger.kernel.org [mailto:netdev-owner@vger.kernel.org] > >On Behalf Of John Fastabend > >Also wouldn't you want an unlikely() in your patch? > > No because it is quite normal to have packet < ETH_ZLEN. e.g. ARP packets. ARP packets ? Hardly a performance problem. Or make sure all these packets have enough tailroom, or else you are going to hit the cost of reallocating packets. I would better point TCP pure ACK packets, since their size can be 54 bytes. diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index cfe6ffe..aefc681 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -3083,8 +3083,9 @@ void tcp_send_ack(struct sock *sk) /* We are not putting this on the write queue, so * tcp_transmit_skb() will set the ownership to this * sock. + * Add 64 bytes of tailroom so that some drivers can use skb_pad() */ - buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC)); + buff = alloc_skb(MAX_TCP_HEADER + 64, sk_gfp_atomic(sk, GFP_ATOMIC)); if (buff == NULL) { inet_csk_schedule_ack(sk); inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;