[RFC] Fixing CPU Hotplug for RealView Platforms

[Russell King - ARM Linux]

On Mon, Dec 20, 2010 at 09:16:15AM +0100, Vincent Guittot wrote:
> I'm also interested in hotplug latency measurement and have done some
> on my CA9 platform u8500. I have the same kind of result for plugging
> a secondary cpu:
>   total duration = 295ms
>   166 us for the low level cpu wake up
>   228ms between the return from platform_cpu_die and the cpu becomes online
> 
> I have added some trace events for doing these measurements and I'd
> like to add some generic traces point in the cpu hotplug code like we
> already have in power management code (cpuidle, suspend, cpufreq ...)
> These traces could be used with power events for studying the impact
> of cpu hotplug in the complete power management scheme.

Note that if you pass lpj=<number> to the kernel, you'll bypass the
calibration and have a faster response to CPU onlining.