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

  • To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
  • From: harish <mvharish@xxxxxxxxx>
  • Date: Mon, 12 Jun 2006 12:05:24 -0700
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Mon, 12 Jun 2006 12:05:48 -0700
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Hi Keir,
Thanks a lot. I shall sync up to the latest unstable then. Shall keep you posted on how it goes.


On 6/11/06, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:

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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