Re: [PATCH 2/2] smp_call_function: use rwlocks on queues rather thanrcu

[Jeremy Fitzhardinge]

Andi Kleen wrote:
> Right now my impression is that it is not well understood why
> the kmalloc makes the IPI that much slower. In theory a kmalloc
> shouldn't be all that slow, it's essentially just a 
> "disable interrupts; unlink object from cpu cache; enable interrupts"
> with some window dressing. kfree() is similar.
>
> Does it bounce a cache line on freeing perhaps?

I think it's just an assumption that it would be slower.  Has anyone
measured it?

(Note: The measurements I posted do not cover this path, because it was
on a two cpu system, and it was always using the call-single path.)

    J
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