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Re: [Xen-devel] Question Also regarding interrupt balancing

On 10 Jun 2006, at 17:58, harish wrote:

echo "2" > /proc/irq/23/smp_affinity  does not seem to change the value in smp_affinity
 cat /proc/irq/23/smp_affinity still shows 0f

 Could there some bug or configuration problem that you can think of?

It was a bug, which I've just fixed in -unstable and -testing staging trees. When that reaches the public trees you should find that writing to smp_affinity has the usual effect, but note: 1. As when running on native, a request to change affinity is not processed until the next interrupt occurs for that irq. If the interrupt rate on that irq is very low, you may be able to observe old value in smp_affinity before it is changed. 2. You cannot change affinity of CPU-local interrupts (timer, resched, callfunc). Requests to do so are silently ignored. 3. If you try to set a multi-cpu cpumask for affinity, it will be changed to a single-cpu cpumask automatically. Linux-on-Xen does not automatically balance irq load across cpus -- that has to be done by a user-space daemon (e.g., irqbalance).

 -- Keir

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