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>

diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 8f7788d..871f9e2 100644 (file)
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -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 */