[PATCH] genirq: Set initial default irq affinity to just CPU0

[David Miller]

From: "Chris Friesen" <cfriesen at nortel.com>
Date: Mon, 27 Oct 2008 11:36:21 -0600

> David Miller wrote:
> > From: Kevin Diggs <kevdig at hypersurf.com>
> > Date: Sat, 25 Oct 2008 15:53:46 -0700
> > 
> >> What does this all mean to my GigE (dual 1.1 GHz 7455s)? Is this
> >> thing supposed to be able to spread irq between its cpus?
> > Networking interrupts should lock onto a single CPU, unconditionally.
> > That's the optimal way to handle networking interrupts, especially
> > with multiqueue chips.
> 
> What about something like the Cavium Octeon, where we have 16 cores but a single core isn't powerful enough to keep up with a gigE device?

Hello, we either have hardware that does flow seperation and has multiple RX queues
going to multiple MSI-X interrupts or we do flow seperation in software (work
in progress patches were posted for that about a month ago, maybe something final
will land in 2.6.29)

Just moving the interrupt around when not doing flow seperation is as
suboptimal as you can possibly get.  You'll get out of order packet
processing within the same flow, TCP will retransmit when the
reordering gets deep enough, and then you're totally screwed
performance wise.