Re: [RFC/PATCH] cpuset: cpuset irq affinities

[Ingo Molnar]

* Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:

> > Could you educate me a little, Peter, on what these irqs are and on 
> > the sorts of ways people might want to place them across CPUs?
> 
> I'm not sure I know what you're asking. IRQ are hardware notifiers and 
> do all kinds of things depending on the hardware. Network cards 
> typically use them to notify the CPU of incoming packets. Video cards 
> can do vsync notifiers, empty dma buffers, whatnot.

irq affinity masks can basically be thought of as: "these are the CPUs 
where external hardware events will trigger certain kernel functions and 
cause overhead on those CPUs". An IRQ can have followup effects: softirq 
execution, workqueue execution, etc.

so managing the IRQ masks is very meaningful and just as meaningful as 
managing the affinity masks of tasks. You can think of "IRQ# 123" as 
"special kernel task # 123".

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/