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

Peter Zijlstra
2012-02-15T09:26:16Z

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.