From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751150AbaJAEYv (ORCPT ); Wed, 1 Oct 2014 00:24:51 -0400 Received: from mail-pa0-f48.google.com ([209.85.220.48]:47245 "EHLO mail-pa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750861AbaJAEYt (ORCPT ); Wed, 1 Oct 2014 00:24:49 -0400 Message-ID: <1412137489.16704.26.camel@edumazet-glaptop2.roam.corp.google.com> Subject: Re: [PATCH net v6 4/4] tg3: Fix tx_pending checks for tg3_tso_bug From: Eric Dumazet To: Prashant Cc: David Miller , bpoirier@suse.de, mchan@broadcom.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 30 Sep 2014 21:24:49 -0700 In-Reply-To: <542B71B1.4020103@broadcom.com> References: <1409960135.18724.33.camel@prashant> <1409961810.26422.149.camel@edumazet-glaptop2.roam.corp.google.com> <20140905.171306.1460013939580748402.davem@davemloft.net> <20140905.213902.1124686922505260665.davem@davemloft.net> <542B71B1.4020103@broadcom.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2014-09-30 at 20:14 -0700, Prashant wrote: > Sorry about the late reply, out of all the HW bug conditions checked in > tg3_tx_frag_set() the most frequently hit condition is the short 8 byte > dma bug, where the chip cannot handle TX descriptors whose data buffer > is 8 bytes or less. Most of the LSO skb's given to the driver has their > fragments filled upto PAGE_SIZE (expect the last fragment depending on > skb->len). And if such a LSO skb's last fragment meets the 8 bytes HW > bug condition the above routine will not help workaround this particular > case. Thats pretty easy to work around. Say rebuilt skb has N frags (N > 1 given your description) They are numbered 0, ... N-2, N-1 Instead of filling N-2 completely, fill it to PAGE_SIZE-8, so that last frag has at least 8 bytes in it. Also take a look at commit 2e4e44107176d552f8bb1bb76053e850e3809841 ("net: add alloc_skb_with_frags() helper")