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cpuidle: Add new macro to enter a retention idle state 

If a CPU is entering a low power idle state where it doesn't lose any
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 idle states.

CPU_PM_CPU_IDLE_ENTER_RETENTION assumes that no state is lost and
hence CPU PM notifiers will not be called. We may need a broader
change if we need to support partial retention states effeciently.

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
        Average overhead of cpu_pm_enter - 1.2us
        Average overhead of cpu_pm_exit  - 3.1us

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Prashanth Prakash 2017-11-15 10:11:49 -07:00 committed by Catalin Marinas
parent 1f911c3a11
commit db50a74d81
1 changed files with 24 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
include/linux/cpuidle.h
View File

@ -257,22 +257,30 @@ static inline int cpuidle_register_governor(struct cpuidle_governor *gov)
{return 0;}
#endif
#define CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx) \
({ \
int __ret; \
\
if (!idx) { \
cpu_do_idle(); \
return idx; \
} \
\
__ret = cpu_pm_enter(); \
if (!__ret) { \
__ret = low_level_idle_enter(idx); \
cpu_pm_exit(); \
} \
\
__ret ? -1 : idx; \
#define __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, is_retention) \
({ \
int __ret = 0; \
\
if (!idx) { \
cpu_do_idle(); \
return idx; \
} \
\
if (!is_retention) \
__ret = cpu_pm_enter(); \
if (!__ret) { \
__ret = low_level_idle_enter(idx); \
if (!is_retention) \
cpu_pm_exit(); \
} \
\
__ret ? -1 : idx; \
})
#define CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx) \
__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, 0)
#define CPU_PM_CPU_IDLE_ENTER_RETENTION(low_level_idle_enter, idx) \
__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, 1)
#endif /* _LINUX_CPUIDLE_H */