From mboxrd@z Thu Jan 1 00:00:00 1970 From: Prashant Subject: Re: [PATCH net v6 4/4] tg3: Fix tx_pending checks for tg3_tso_bug Date: Wed, 1 Oct 2014 11:29:43 -0700 Message-ID: <542C4817.60301@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> <1412137489.16704.26.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit Cc: David Miller , , , , To: Eric Dumazet Return-path: In-Reply-To: <1412137489.16704.26.camel@edumazet-glaptop2.roam.corp.google.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 9/30/2014 9:24 PM, Eric Dumazet wrote: > 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. definitely it can be tweaked to match what is needed with additional workarounds. > > Also take a look at commit 2e4e44107176d552f8bb1bb76053e850e3809841 > ("net: add alloc_skb_with_frags() helper") > > This helper is much modular/flexible than the initial proposed one. Thanks. >