linux-kernel - [PATCH 2.6.26.y] cpuidle: 40000 wake/s unless idle=nomwait

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Message-id: <alpine.LFD.2.00.0902211203430.4051@localhost.localdomain>
Date:	Sat, 21 Feb 2009 12:08:14 -0500 (EST)
From:	Len Brown <lenb@...nel.org>
To:	stable@...nrel.org
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH 2.6.26.y] cpuidle: 40000 wake/s unless idle=nomwait

From: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>

upstream 2.6.27: 320eee776357db52d6fcfb11cff985b1976a4595
"cpuidle: Menu governor fix wrong usage of measured_us"
fixes http://bugzilla.kernel.org/show_bug.cgi?id=10914
"40000 wake/s unless idle=nomwait"


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 <venkatesh.pallipadi@...el.com>
Signed-off-by: Wei Gang <gang.wei@...el.com>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Len Brown <len.brown@...el.com>

---
 drivers/cpuidle/governors/menu.c |   31 +++++++++++++++++++------------
 1 files changed, 19 insertions(+), 12 deletions(-)

Index: linux-2.6.26.y/drivers/cpuidle/governors/menu.c
===================================================================
--- linux-2.6.26.y.orig/drivers/cpuidle/governors/menu.c
+++ linux-2.6.26.y/drivers/cpuidle/governors/menu.c
@@ -67,9 +67,9 @@ 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
@@ -77,20 +77,27 @@ 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;
 	}
 }
 
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