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On Fri, 15 Sep 2000, Bogdan Costescu wrote:

> On Fri, 15 Sep 2000, jamal wrote:
> > You use the period(5-10micros), while waiting
> > for full packet arrival, to make the route decision (lookup etc).
> > i.e this will allow for a better FF; it will not offload things.
>
> Just that you span several layers by doing this, it's not driver specific
> anymore.

Many chips have some sort of early-Rx feature, but it's still a bad idea for
the many reasons I've pointed out before.

An additional reason not use early-Rx is that chips such as the 3c905C are
most efficient at using the PCI bus when transfering a whole packet in a
single PCI burst (plus two smaller bursts initially reading and later
writing the descriptor). Using an early-Rx interrupt scheme means using
multiple smaller bursts.

The early-Rx scheme worked well on the ISA bus, where transfers were slow
and not bursting.

Also note: it is possible to drop an Rx packet after the early Rx
interrupt.

Donald Becker becker@scyld.com
Scyld Computing Corporation http://www.scyld.com
410 Severn Ave. Suite 210 Beowulf-II Cluster Distribution
Annapolis MD 21403

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