Re: bisected: 'perf top' causing soft lockups under Xen

[Peter Zijlstra]

On Wed, 2012-02-15 at 00:57 -0800, Steven Noonan wrote:
> It seems to me that there are two options for fixing this, but I'm
> probably lacking the necessary context (or experience with Xen). Either:
> 
> - The patch provided by Ben needs to have additional work to specially
>   handle IRQ_WORK_VECTOR, since it seems to be a special case where
>   there's no event channel attached for it. Perhaps adding an event
>   channel for this is the fix? Seems high-overhead, but I lack a good
>   understanding of how interrupts are handled in Xen.

So that's a self-IPI, is Xen failing to implement this?

> or
> 
> - Perf needs to be "enlightened" about Xen and avoid sending an IPI in
>   the first place.

Uhm, no. If anything Xen should simply not implement
arch_irq_work_raise(). The callbacks are then ran from the timer
interrupt.
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