Re: [e1000 2.6 10/11] TxDescriptors -> 1024 default

[Jeff Garzik <jgarzik@xxxxxxxxx>]

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.
        Jeff