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

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Date:   Sat, 14 Oct 2017 03:01:28 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Aubrey Li <aubrey.li@...el.com>
Cc:     tglx@...utronix.de, peterz@...radead.org, len.brown@...el.com,
        ak@...ux.intel.com, tim.c.chen@...ux.intel.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, Aubrey Li <aubrey.li@...ux.intel.com>
Subject: Re: [RFC PATCH v2 7/8] cpuidle: introduce irq timing to make idle prediction

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@...ux.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();
>  		/*
>