On Wed, Nov 15, 2017 at 10:11:48AM -0700, Prashanth Prakash wrote:

CPU_PM_CPU_IDLE_ENTER() treats all idle states whose idx != 0 as a
state that loses some context, but we can have deeper idle states that
doesn't lose any software context. If a CPU is entering such a low power
idle state where it retains the context, then there is no need to call
cpu_pm_enter()/cpu_pm_exit().

Add a new macro(CPU_PM_CPU_IDLE_ENTER_RETENTION) to be used by cpuidle
drivers when they are entering retention state. By not calling cpu_pm_enter
and cpu_pm_exit we reduce the latency involved in entering and exiting
the retention states.

On ARM64 based Qualcomm server platform we measured below overhead for
for calling cpu_pm_enter and cpu_pm_exit for retention states.

workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
Overhead of cpu_pm_enter - 1.2us(Average), 6.5us(Max)
Overhead of cpu_pm_exit  - 3.1us(Average), 11.1us(Max)

I queued the patches in the arm64 tree for 4.16. Thanks.

-- 
Catalin