| Message ID | 1510187922-8218-2-git-send-email-pprakash@codeaurora.org (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
On 09/11/17 00:38, Prashanth Prakash wrote: > 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. > > 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 > Just add a description to inform that if retention is enabled, it's assumed to be full retention(IOW no state needs to be saved/restored) and hence the CPU PM notifiers are not called. We may need to change this in case we need to support partial retention states in future. Other than that, Acked-by: Sudeep Holla <sudeep.holla@arm.com>
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h index 8f7788d..871f9e2 100644 --- 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 */
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. 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 Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org> --- include/linux/cpuidle.h | 40 ++++++++++++++++++++++++---------------- 1 file changed, 24 insertions(+), 16 deletions(-)