Re: [PATCH 05/10] smp: Fast path check on IPI list

[Peter Zijlstra]

On Mon, Jul 28, 2014 at 07:37:31PM +0200, Frederic Weisbecker wrote:
> When we enqueue a remote irq work, we trigger the same IPI as those
> raised by smp_call_function_*() family.
> 
> So when we receive such IPI, we check both irq_work and smp_call_function
> queues. Thus if we trigger a remote irq work, we'll likely find the
> smp_call_function queue empty unless we collide with concurrent enqueuers
> but the probability is low.
> 
> Meanwhile, checking the smp_call_function queue can be costly because
> we use llist_del_all() which relies on cmpxchg().

xchg()
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