[RFC] Fixing CPU Hotplug for RealView Platforms

Vincent Guittot vincent.guittot at linaro.org
Mon Jan 3 12:39:56 EST 2011

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

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