Re: [RFC PATCH v2 7/8] cpuidle: introduce irq timing to make idle prediction

Rafael J. Wysocki
2017-10-14T01:11:02Z

On Saturday, September 30, 2017 9:20:33 AM CEST Aubrey Li wrote:
> Introduce irq timings output as a factor to predict the duration
> of the coming idle
>
> Signed-off-by: Aubrey Li <aubrey.li@linux.intel.com>
> ---
> drivers/cpuidle/Kconfig | 1 +
> drivers/cpuidle/cpuidle.c | 17 ++++++++++++++++-
> 2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
> index 7e48eb5..8b07e1c 100644
> --- a/drivers/cpuidle/Kconfig
> +++ b/drivers/cpuidle/Kconfig
> @@ -5,6 +5,7 @@ config CPU_IDLE
> default y if ACPI || PPC_PSERIES
> select CPU_IDLE_GOV_LADDER if (!NO_HZ && !NO_HZ_IDLE)
> select CPU_IDLE_GOV_MENU if (NO_HZ || NO_HZ_IDLE)
> + select IRQ_TIMINGS
> help
> CPU idle is a generic framework for supporting software-controlled
> idle processor power management. It includes modular cross-platform
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 5d4f0b6..be56cea 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -22,6 +22,7 @@
> #include <linux/module.h>
> #include <linux/suspend.h>
> #include <linux/tick.h>
> +#include <linux/interrupt.h>
> #include <trace/events/power.h>
>
> #include "cpuidle.h"
> @@ -342,13 +343,27 @@ void cpuidle_entry_end(void)
> void cpuidle_predict(void)
> {
> struct cpuidle_device *dev = cpuidle_get_device();
> - unsigned int overhead_threshold;
> + unsigned int idle_interval, overhead_threshold;
> + u64 now, next_evt;
>
> if (!dev)
> return;
>
> overhead_threshold = dev->idle_stat.overhead * sysctl_fast_idle_ratio;
>
> + /*
> + * check irq timings if the next event is coming soon
> + */
> + now = local_clock();
> + local_irq_disable();
> + next_evt = irq_timings_next_event(now);
> + local_irq_enable();
> + idle_interval = div_u64(next_evt - now, NSEC_PER_USEC);

Another division ...

> + if (idle_interval < overhead_threshold) {
> + dev->idle_stat.fast_idle = true;
> + return;
> + }
> +
> if (cpuidle_curr_governor->predict) {
> dev->idle_stat.predicted_us = cpuidle_curr_governor->predict();
> /*
>