From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [net-next 03/12] i40e: Handle a single mss packet with more than 8 frags Date: Mon, 17 Nov 2014 08:45:17 -0800 Message-ID: <1416242717.5102.16.camel@edumazet-glaptop2.roam.corp.google.com> References: <1416031715-32498-1-git-send-email-jeffrey.t.kirsher@intel.com> <1416031715-32498-4-git-send-email-jeffrey.t.kirsher@intel.com> <1416075695.17262.86.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: "Kirsher, Jeffrey T" , "davem@davemloft.net" , "Kong, Serey" , "netdev@vger.kernel.org" , "nhorman@redhat.com" , "sassmann@redhat.com" , "jogreene@redhat.com" To: "Nelson, Shannon" Return-path: Received: from mail-ie0-f175.google.com ([209.85.223.175]:34742 "EHLO mail-ie0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751483AbaKQQpN (ORCPT ); Mon, 17 Nov 2014 11:45:13 -0500 Received: by mail-ie0-f175.google.com with SMTP id at20so6916141iec.34 for ; Mon, 17 Nov 2014 08:45:12 -0800 (PST) In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 2014-11-17 at 16:04 +0000, Nelson, Shannon wrote: > This typically hits when there are many little TSO packets in a single > MTU size frame. The hardware doesn't like dealing with more than 8 > separate buffers. > > If skb_linearize() fails and we try to send the skb as is, the > hardware will throw an MDD event and disable that particular queue, > possibly causing a Tx hang, which will lead to a PF reset and then we > continue on. It's a bit of a hit to throughput, and most folks get a > little annoyed when seeing the Tx hang stack trace in their log, but > it generally isn't fatal. > > If we disable the MDD detection, the hardware ends up putting garbage > on the wire. > > It looks to me that the way for skb_linearize() to fail is with > -ENOMEM, in which case we probably have other issues. > This kind of events happens in real workloads, trust me. > If there are some alternative suggestions for dealing with this, we'd > be happy to hear about them. Nelson, all you have to do is to check skb_linearize(skb) return code. If its a failure, then drop this packet. How hard is this ? This should hardly trigger in normal conditions. If some customer complains, then you might implement something more complex in the future. Lets fix the bug first in a 100% safe way.