[RFC] Fixing CPU Hotplug for RealView Platforms

[Vincent Guittot]

On 3 January 2011 11:46, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> 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.
>

yes, the total duration decreases down to 40ms