Re: [patch 4/10] s390: network driver.

From: Jeff Garzik
Date: Sat Nov 13 2004 - 20:31:16 EST

Thomas Spatzier wrote:

You should be using netif_carrier_{on,off} properly, and not drop the
packets. When (if) link comes back, you requeue the packets to hardware
(or hypervisor or whatever). Your dev->stop() should stop operation and
clean up anything left in your send/receive {rings | buffers}.

When we do not drop packets, but call netif_stop_queue the write queues
of all sockets associated to the net device are blocked as soon as they
get full. This causes problems with programs such as the zebra routing
daemon. So we have to keep the netif queue running in order to not block
any programs.

This is very, very wrong. You are essentially creating in in-driver /dev/null simulator. This does nothing but chew CPU cycles by having the driver drop packets, rather than allowing the system to work as it should.

Queues are DESIGNED to fill up under various conditions.

Would not the zebra routing software have the same problems with cable pull under an e1000 or tg3 gigabit NIC?

We also had a look at some other drivers and the common behaviour seems to
be that packets are lost if the network cable is pulled out.

Which drivers, specifically, are these?

The most popular drivers -- e1000, tg3, etc. -- do not do this, for very good reasons.


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