Re: [PATCH] Add decaying history logic to cpuidle menu idle predictor

[Len Brown <lenb@kernel.org>]

applied

-- Len Brown, Intel Open Source Technology Center

On Tue, 30 Dec 2008, Pallipadi, Venkatesh wrote:

> 
> Add decaying history of predicted idle time, instead of using the last early
> wakeup. This logic helps menu governor do better job of predicting idle time.
> 
> With this change, we also measured noticable (~8%) power savings on
> a DP server system with CPUs supporting deep C states, when system
> was lightly loaded. There was no change to power or perf on other load
> conditions.
> 
> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
> 
> ---
>  drivers/cpuidle/governors/menu.c |   10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6/drivers/cpuidle/governors/menu.c
> ===================================================================
> --- linux-2.6.orig/drivers/cpuidle/governors/menu.c	2008-11-10 15:27:13.000000000 -0800
> +++ linux-2.6/drivers/cpuidle/governors/menu.c	2008-12-30 14:39:15.000000000 -0800
> @@ -15,12 +15,14 @@
>  #include <linux/tick.h>
>  
>  #define BREAK_FUZZ	4	/* 4 us */
> +#define PRED_HISTORY_PCT	50
>  
>  struct menu_device {
>  	int		last_state_idx;
>  
>  	unsigned int	expected_us;
>  	unsigned int	predicted_us;
> +	unsigned int    current_predicted_us;
>  	unsigned int	last_measured_us;
>  	unsigned int	elapsed_us;
>  };
> @@ -47,6 +49,12 @@ static int menu_select(struct cpuidle_de
>  	data->expected_us =
>  		(u32) ktime_to_ns(tick_nohz_get_sleep_length()) / 1000;
>  
> +	/* Recalculate predicted_us based on prediction_history_pct */
> +	data->predicted_us *= PRED_HISTORY_PCT;
> +	data->predicted_us += (100 - PRED_HISTORY_PCT) *
> +				data->current_predicted_us;
> +	data->predicted_us /= 100;
> +
>  	/* find the deepest idle state that satisfies our constraints */
>  	for (i = CPUIDLE_DRIVER_STATE_START + 1; i < dev->state_count; i++) {
>  		struct cpuidle_state *s = &dev->states[i];
> @@ -97,7 +105,7 @@ static void menu_reflect(struct cpuidle_
>  		measured_us = -1;
>  
>  	/* Predict time until next break event */
> -	data->predicted_us = max(measured_us, data->last_measured_us);
> +	data->current_predicted_us = max(measured_us, data->last_measured_us);
>  
>  	if (last_idle_us + BREAK_FUZZ <
>  	    data->expected_us - target->exit_latency) {
> --
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