Re: [Eas-dev] [PATCH V3 2/3] cpufreq: schedutil: Process remote callback for shared policies

[Saravana Kannan]

On 07/20/2017 05:22 AM, Peter Zijlstra wrote:
> So the typical implementation of fast switching we're thinking of is the
> CPU writing the DVFS request into a machine register. Now machine
> registers are typically per logical CPU.

Writing to a memory addressable register. AFAIK, ARM has no support for 
a machine register for DVFS request. So, even if any ARM licensee wants 
to add one, it won't be possible.

Also, even if we have an ARM CPU with a machine register, rejecting a 
valid frequency switch just because it happened to come on a different 
CPU seem silly (you can have a huge performance hit due to that). A much 
better solution is to just make an IPI to the right CPU and execute the 
machine register write on the right CPU.

-Saravana

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