From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: [e1000 2.6 10/11] TxDescriptors -> 1024 default Date: Thu, 11 Sep 2003 15:59:31 -0400 Sender: netdev-bounce@oss.sgi.com Message-ID: <3F60D423.4040005@pobox.com> References: <3F60CA6D.9090503@pobox.com> <3F60D0F3.8080006@candelatech.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: "Feldman, Scott" , netdev@oss.sgi.com, ricardoz@us.ibm.com Return-path: To: Ben Greear In-Reply-To: <3F60D0F3.8080006@candelatech.com> Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org Ben Greear wrote: > Jeff Garzik wrote: > >> Feldman, Scott wrote: >> >>> * Change the default number of Tx descriptors from 256 to 1024. >>> Data from [ricardoz@us.ibm.com] shows it's easy to overrun >>> the Tx desc queue. >> >> >> >> >> All e1000 patches applied except this one. >> >> Of _course_ it's easy to overrun the Tx desc queue. That's why we >> have a TX queue sitting on top of the NIC's hardware queue. And TCP >> socket buffers on top of that. And similar things. >> >> Descriptor increases like this are usually the result of some >> sillyhead blasting out UDP packets, and then wondering why he sees >> packet loss on the local computer (the "blast out packets" side). > > > Erm, shouldn't the local machine back itself off if the various > queues are full? Some time back I looked through the code and it > appeared to. If not, I think it should. Given the guarantees of the protocol, the net stack has the freedom to drop UDP packets, for example at times when (for TCP) one would otherwise queue a packet for retransmit. Jeff