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cpuilde: Misc bug fixes

PATCH New [email protected] 1 participant 4 messages Jul 31, 2008 CPU idle time management framework

lore
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#1 lore raw

PATCH 1/3 cpuidle: Do not use poll_idle unless user asks for it

poll_idle was added to CPUIDLE, just as a low latency idle handler, to be used in cases when user desires CPUs not to enter any idle state at all. It was supposed to be a run time idle=poll option to the user. But, it was indeed getting used during normal menu and ladder governor default case, with no special user setting (Reported by Linus Torvalds).

Change below ensures that poll_idle will not be used unless user explicitly asks pm_qos infrastructure for zero latency requirement.

Signed-off-by Venkatesh Pallipadi <[email protected]>
---
 drivers/cpuidle/governors/ladder.c |   14 ++++++++++----
 drivers/cpuidle/governors/menu.c   |   11 +++++++++--
 2 files changed, 19 insertions(+), 6 deletions(-)
drivers/cpuidle/governors/menu.c +9 -2
Index: linux-2.6/drivers/cpuidle/governors/menu.c
===================================================================
@@ -34,21 +34,28 @@ static DEFINE_PER_CPU(struct menu_device
 static int menu_select(struct cpuidle_device *dev)
 {
 	struct menu_device *data = &__get_cpu_var(menu_devices);
+	int latency_req = pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY);
 	int i;
 
+	/* Special case when user has set very strict latency requirement */
+	if (unlikely(latency_req == 0)) {
+		data->last_state_idx = 0;
+		return 0;
+	}
+
 	/* determine the expected residency time */
 	data->expected_us =
 		(u32) ktime_to_ns(tick_nohz_get_sleep_length()) / 1000;
 
 	/* find the deepest idle state that satisfies our constraints */
-	for (i = 1; i < dev->state_count; i++) {
+	for (i = CPUIDLE_DRIVER_STATE_START + 1; i < dev->state_count; i++) {
 		struct cpuidle_state *s = &dev->states[i];
 
 		if (s->target_residency > data->expected_us)
 			break;
 		if (s->target_residency > data->predicted_us)
 			break;
-		if (s->exit_latency > pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY))
+		if (s->exit_latency > latency_req)
 			break;
 	}
drivers/cpuidle/governors/ladder.c +10 -4
Index: linux-2.6/drivers/cpuidle/governors/ladder.c
===================================================================
@@ -67,10 +67,17 @@ static int ladder_select_state(struct cp
 	struct ladder_device *ldev = &__get_cpu_var(ladder_devices);
 	struct ladder_device_state *last_state;
 	int last_residency, last_idx = ldev->last_state_idx;
+	int latency_req = pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY);
 
 	if (unlikely(!ldev))
 		return 0;
 
+	/* Special case when user has set very strict latency requirement */
+	if (unlikely(latency_req == 0)) {
+		ladder_do_selection(ldev, last_idx, 0);
+		return 0;
+	}
+
 	last_state = &ldev->states[last_idx];
 
 	if (dev->states[last_idx].flags & CPUIDLE_FLAG_TIME_VALID)

@@ -81,8 +88,7 @@ static int ladder_select_state(struct cp
 	/* consider promotion */
 	if (last_idx < dev->state_count - 1 &&
 	    last_residency > last_state->threshold.promotion_time &&
-	    dev->states[last_idx + 1].exit_latency <=
-			pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY)) {
+	    dev->states[last_idx + 1].exit_latency <= latency_req) {
 		last_state->stats.promotion_count++;
 		last_state->stats.demotion_count = 0;
 		if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {

@@ -92,7 +98,7 @@ static int ladder_select_state(struct cp
 	}
 
 	/* consider demotion */
-	if (last_idx > 0 &&
+	if (last_idx > CPUIDLE_DRIVER_STATE_START &&
 	    last_residency < last_state->threshold.demotion_time) {
 		last_state->stats.demotion_count++;
 		last_state->stats.promotion_count = 0;

@@ -117,7 +123,7 @@ static int ladder_enable_device(struct c
 	struct ladder_device_state *lstate;
 	struct cpuidle_state *state;
 
-	ldev->last_state_idx = 0;
+	ldev->last_state_idx = CPUIDLE_DRIVER_STATE_START;
 
 	for (i = 0; i < dev->state_count; i++) {
 		state = &dev->states[i];
author
#2 lore raw

PATCH 2/3 cpuidle: Menu governor fix wrong usage of measured_us

In reply to [email protected]

There is a bug in menu governor where we have

		if (data->elapsed_us < data->elapsed_us + measured_us)

with measured_us already having elapsed_us added in tickless case here

	unsigned int measured_us =
		cpuidle_get_last_residency(dev) + data->elapsed_us;

Also, it should be last_residency, not measured_us, that need to be used to do comparing and distinguish between expected & non-expected events.

Refactor menu_reflect() to fix these two problems.

Signed-off-by Venkatesh Pallipadi <[email protected]>
Signed-off-by Wei Gang <[email protected]>
---
 drivers/cpuidle/governors/menu.c |   31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)
drivers/cpuidle/governors/menu.c +19 -12
Index: linux-2.6/drivers/cpuidle/governors/menu.c
===================================================================
@@ -74,9 +74,9 @@ static void menu_reflect(struct cpuidle_
 {
 	struct menu_device *data = &__get_cpu_var(menu_devices);
 	int last_idx = data->last_state_idx;
-	unsigned int measured_us =
-		cpuidle_get_last_residency(dev) + data->elapsed_us;
+	unsigned int last_idle_us = cpuidle_get_last_residency(dev);
 	struct cpuidle_state *target = &dev->states[last_idx];
+	unsigned int measured_us;
 
 	/*
 	 * Ugh, this idle state doesn't support residency measurements, so we

@@ -84,20 +84,27 @@ static void menu_reflect(struct cpuidle_
 	 * for one full standard timer tick.  However, be aware that this
 	 * could potentially result in a suboptimal state transition.
 	 */
-	if (!(target->flags & CPUIDLE_FLAG_TIME_VALID))
-		measured_us = USEC_PER_SEC / HZ;
+	if (unlikely(!(target->flags & CPUIDLE_FLAG_TIME_VALID)))
+		last_idle_us = USEC_PER_SEC / HZ;
 
-	/* Predict time remaining until next break event */
-	if (measured_us + BREAK_FUZZ < data->expected_us - target->exit_latency) {
-		data->predicted_us = max(measured_us, data->last_measured_us);
+	/*
+	 * measured_us and elapsed_us are the cumulative idle time, since the
+	 * last time we were woken out of idle by an interrupt.
+	 */
+	if (data->elapsed_us <= data->elapsed_us + last_idle_us)
+		measured_us = data->elapsed_us + last_idle_us;
+	else
+		measured_us = -1;
+
+	/* Predict time until next break event */
+	data->predicted_us = max(measured_us, data->last_measured_us);
+
+	if (last_idle_us + BREAK_FUZZ <
+	    data->expected_us - target->exit_latency) {
 		data->last_measured_us = measured_us;
 		data->elapsed_us = 0;
 	} else {
-		if (data->elapsed_us < data->elapsed_us + measured_us)
-			data->elapsed_us = measured_us;
-		else
-			data->elapsed_us = -1;
-		data->predicted_us = max(measured_us, data->last_measured_us);
+		data->elapsed_us = measured_us;
 	}
 }
author
#3 lore raw

PATCH 3/3 cpuidle: Make ladder governor honor latency requirements fully

In reply to [email protected]

ladder governor only honored latency requirement when promoting C-states. Instead. it should check for latency requirement on each idle call, and demote to appropriate C-state when there is a latency requirement change.

Signed-off-by Venkatesh Pallipadi <[email protected]>
---
 drivers/cpuidle/governors/ladder.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)
drivers/cpuidle/governors/ladder.c +12 -0
Index: linux-2.6/drivers/cpuidle/governors/ladder.c
===================================================================
@@ -99,6 +99,18 @@ static int ladder_select_state(struct cp
 
 	/* consider demotion */
 	if (last_idx > CPUIDLE_DRIVER_STATE_START &&
+	    dev->states[last_idx].exit_latency > latency_req) {
+		int i;
+
+		for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) {
+			if (dev->states[i].exit_latency <= latency_req)
+				break;
+		}
+		ladder_do_selection(ldev, last_idx, i);
+		return i;
+	}
+
+	if (last_idx > CPUIDLE_DRIVER_STATE_START &&
 	    last_residency < last_state->threshold.demotion_time) {
 		last_state->stats.demotion_count++;
 		last_state->stats.promotion_count = 0;