Re: [RFC/PATCH] notify user-level IRQ balancer when kernel assigns IRQ affinity

[David Miller <davem@davemloft.net>]

From: Arthur Kepner <akepner@sgi.com>
Date: Fri, 3 Sep 2010 14:05:54 -0700

> 
> We've run into situations where a CPU runs out of interrupt 
> vectors, because all the interrupts are getting the default 
> affinity (and the interrupt balancer hasn't yet run).
> 
> The following emits a netlink message whenever an interrupt 
> is given a default CPU affinity. A user-level IRQ balancer 
> can use those messages to decide if, and how to reassign 
> affinities. This should allow us to avoid running out of 
> vectors on any particular CPU (or at least make it far less 
> likely).
> 
> I know this needs work, but would like to get comments on 
> the idea before doing more coding and testing.
> 
> Signed-off-by: Arthur Kepner <akepner@sgi.com>

As I replied to you on netdev, this can't possibly work.

Interrupt allocation needs to work properly before userspace
even starts up.  So the allocation management must be inside
of the kernel entirely.