linux-kernel - [RFC PATCH v2 1/8] cpuidle: menu: extract prediction functionality

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Date:   Sat, 30 Sep 2017 15:20:27 +0800
From:   Aubrey Li <aubrey.li@...el.com>
To:     tglx@...utronix.de, peterz@...radead.org, rjw@...ysocki.net,
        len.brown@...el.com, ak@...ux.intel.com, tim.c.chen@...ux.intel.com
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Aubrey Li <aubrey.li@...el.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>
Subject: [RFC PATCH v2 1/8] cpuidle: menu: extract prediction functionality

There are several factors in the menu governor to predict the next
idle interval:
- the next timer
- the recent idle interval history
- the corrected idle interval pattern
These factors are common enough to be extracted to be one function.

Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
---
 drivers/cpuidle/governors/menu.c | 64 +++++++++++++++++++++++++---------------
 1 file changed, 40 insertions(+), 24 deletions(-)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 61b64c2..6bed197 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -276,6 +276,45 @@ static unsigned int get_typical_interval(struct menu_device *data)
 }
 
 /**
+ * menu_predict - predict the coming idle interval
+ *
+ * Return the predicted coming idle interval in micro-second
+ */
+static unsigned int menu_predict(void)
+{
+	struct menu_device *data = this_cpu_ptr(&menu_devices);
+	unsigned int expected_interval;
+	int cpu = smp_processor_id();
+
+	if (!data)
+		return UINT_MAX;
+
+	/* determine the expected residency time, round up */
+	data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length());
+
+	data->bucket = which_bucket(data->next_timer_us, nr_iowait_cpu(cpu));
+
+	/*
+	 * Force the result of multiplication to be 64 bits even if both
+	 * operands are 32 bits.
+	 * Make sure to round up for half microseconds.
+	 */
+	data->predicted_us = DIV_ROUND_CLOSEST_ULL((uint64_t)
+		data->next_timer_us * data->correction_factor[data->bucket],
+		RESOLUTION * DECAY);
+
+	expected_interval = get_typical_interval(data);
+	expected_interval = min(expected_interval, data->next_timer_us);
+
+	/*
+	 * Use the lowest expected idle interval to pick the idle state.
+	 */
+	data->predicted_us = min(data->predicted_us, expected_interval);
+
+	return data->predicted_us;
+}
+
+/**
  * menu_select - selects the next idle state to enter
  * @drv: cpuidle driver containing state data
  * @dev: the CPU
@@ -289,7 +328,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	int first_idx;
 	int idx;
 	unsigned int interactivity_req;
-	unsigned int expected_interval;
 	unsigned long nr_iowaiters, cpu_load;
 	int resume_latency = dev_pm_qos_raw_read_value(device);
 
@@ -306,24 +344,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	if (unlikely(latency_req == 0))
 		return 0;
 
-	/* determine the expected residency time, round up */
-	data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length());
-
-	get_iowait_load(&nr_iowaiters, &cpu_load);
-	data->bucket = which_bucket(data->next_timer_us, nr_iowaiters);
-
-	/*
-	 * Force the result of multiplication to be 64 bits even if both
-	 * operands are 32 bits.
-	 * Make sure to round up for half microseconds.
-	 */
-	data->predicted_us = DIV_ROUND_CLOSEST_ULL((uint64_t)data->next_timer_us *
-					 data->correction_factor[data->bucket],
-					 RESOLUTION * DECAY);
-
-	expected_interval = get_typical_interval(data);
-	expected_interval = min(expected_interval, data->next_timer_us);
-
 	if (CPUIDLE_DRIVER_STATE_START > 0) {
 		struct cpuidle_state *s = &drv->states[CPUIDLE_DRIVER_STATE_START];
 		unsigned int polling_threshold;
@@ -345,14 +365,10 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	}
 
 	/*
-	 * Use the lowest expected idle interval to pick the idle state.
-	 */
-	data->predicted_us = min(data->predicted_us, expected_interval);
-
-	/*
 	 * Use the performance multiplier and the user-configurable
 	 * latency_req to determine the maximum exit latency.
 	 */
+	get_iowait_load(&nr_iowaiters, &cpu_load);
 	interactivity_req = data->predicted_us / performance_multiplier(nr_iowaiters, cpu_load);
 	if (latency_req > interactivity_req)
 		latency_req = interactivity_req;
-- 
2.7.4