|To:||Ben Greear <greearb@xxxxxxxxxxxxxxx>|
|Subject:||Re: [e1000 2.6 10/11] TxDescriptors -> 1024 default|
|From:||Jeff Garzik <jgarzik@xxxxxxxxx>|
|Date:||Thu, 11 Sep 2003 15:59:31 -0400|
|Cc:||"Feldman, Scott" <scott.feldman@xxxxxxxxx>, netdev@xxxxxxxxxxx, ricardoz@xxxxxxxxxx|
|References:||<Pine.LNX.4.44.0309081953510.1261-100000@xxxxxxxxxxxxxxxxxxxxx> <3F60CA6D.9090503@xxxxxxxxx> <3F60D0F3.8080006@xxxxxxxxxxxxxxx>|
|User-agent:||Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2.1) Gecko/20021213 Debian/1.2.1-2.bunk|
Ben Greear wrote:
Jeff Garzik wrote:Feldman, Scott wrote:* Change the default number of Tx descriptors from 256 to 1024. Data from [ricardoz@xxxxxxxxxx] 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.
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