RE: [PATCH] cpuidle: Add "cpuidle.use_deepest" to bypass governor and allow HW to go deep

[Doug Smythies]

On 2017.11.16 08:11 Thomas Ilsche wrote:
> On 2017-11-09 08:38, Len Brown wrote:
>> From: Len Brown <len.brown@xxxxxxxxx>
>> 
>> While there are several mechanisms (cmdline, sysfs, PM_QOS) to limit
>> cpuidle to shallow idle states, there is no simple mechanism
>> to give the hardware permission to enter the deeptest state permitted by PM_QOS.
>> 
>> Here we create the "cpuidle.use_deepest" modparam to provide this capability.
>> 
>> "cpuidle.use_deepest=Y" can be set at boot-time, and
>> /sys/module/cpuidle/use_deepest can be modified (with Y/N) at run-time.
>
> This is a good option to have and can conveniently prevent idle power consumption
> issues. But that wouldn't be a reasonable default, would it?
> I still think there is an inherent need for a heuristic and a corresponding
> mitigation to avoid staying in a sleep state too long.

I think so, yes. The potential energy savings, depending on work flow, are significant.
For the idle state 0 case, I have some supporting data that I will send on
the other e-mail thread.

... Doug