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@xxxxxxxxx>
>
> ---
> 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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