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Re: [Xen-devel] [PATCH] Reuse irq number for virq/ipi after vcpu unplug/plug

  • To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
  • Date: Sun, 04 Feb 2007 04:51:54 +0000
  • Delivery-date: Sat, 03 Feb 2007 20:51:44 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcdHTqIuaJIC5LiAQZGiyexI3PPLIQAyY637
  • Thread-topic: [Xen-devel] [PATCH] Reuse irq number for virq/ipi after vcpu unplug/plug

On 3/2/07 04:49, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> Irq nunmber for per-vcpu event (virq/ipi) needs kept
> accross vcpu plug/unplug, once allocated. We just
> reuse this irq number and bind it to a new event port.
> Or else, /proc/interrupt exports messed statistics
> like:

Noone cares about absolute /proc/interrupt numbers, only rate of change. If
pushed, I would argue that the stats should be zeroed when an interrupt line
is freed (since the interrupt then stops appearing in /proc/interrupts,
which logically implies that the stats lifetime has ended, and so a reuse of
that interrupt is a new lifetime starting from zero). After all, all
irq-evtchn bindings are dynamic running on Xen: a Linux irq may
theoretically get used for all sorts of different devices during the
lifetime of the Linux guest. Should all these uses get aggregated over time?

Zeroing the stats would potentially be a patch for lkml, or we could do it
for dynirqs ourselves in unbind_from_irq(). That's a patch I would accept.

 -- Keir

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