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 -- Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
