Re: [linux-pm] [PATCH] cpuidle: avoid singing capacitors

[Pierre Ossman]

On Wed, 5 Mar 2008 09:40:23 +0100
Pierre Ossman <drzeus-list@xxxxxxxxx> wrote:

> 
> So I need to build some global algorithm instead of one per core. Ideas are welcome.
> 

I'm currently trying this variant. No noise yet, but the time spent in C3 seems to take a massive hit. I'll see if I can get around to some kind of power measurement (ideas for doing that in a sane way are still welcome btw).

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 78d77c5..960aa39 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -16,6 +16,11 @@
 
 #define BREAK_FUZZ	4	/* 4 us */
 
+static unsigned int min_deep_sleep = 0;
+static unsigned int failed_deep = 0;
+
+static unsigned long global_last_deep;
+
 struct menu_device {
 	int		last_state_idx;
 
@@ -23,6 +28,8 @@ struct menu_device {
 	unsigned int	predicted_us;
 	unsigned int	last_measured_us;
 	unsigned int	elapsed_us;
+
+	unsigned long	last_deep;
 };
 
 static DEFINE_PER_CPU(struct menu_device, menu_devices);
@@ -50,9 +57,51 @@ static int menu_select(struct cpuidle_device *dev)
 			break;
 		if (s->exit_latency > pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY))
 			break;
+
+		/*
+		 * In order to avoid the problem of "singing capacitors",
+		 * don't enter a deep sleep for short durations (2 ms seems
+		 * to do the trick). This will, hopefully, keep the problem
+		 * inaudible.
+		 */
+		if (min_deep_sleep && (s->flags & CPUIDLE_FLAG_DEEP)) {
+			if (time_before_eq(jiffies, data->last_deep +
+				HZ * min_deep_sleep / USEC_PER_SEC))
+				break;
+
+			rmb();
+
+			if (time_before_eq(jiffies, global_last_deep +
+				HZ * min_deep_sleep / USEC_PER_SEC))
+				break;
+
+#if 0
+			if (min_deep_sleep > data->expected_us)
+				break;
+			if (min_deep_sleep > cpuidle_get_last_residency(dev))
+				break;
+#endif
+#if 0
+			if (min_deep_sleep > data->predicted_us)
+				break;
+			if (min_deep_sleep > data->last_measured_us)
+				break;
+#endif
+		}
 	}
 
 	data->last_state_idx = i - 1;
+
+	if (dev->states[i - 1].flags & CPUIDLE_FLAG_DEEP) {
+#if 0
+		printk("Sleep interval: %ld jiffies\n",
+			jiffies - data->last_deep);
+#endif
+		data->last_deep = jiffies;
+		global_last_deep = jiffies;
+		wmb();
+	}
+
 	return i - 1;
 }
 
@@ -80,6 +129,15 @@ static void menu_reflect(struct cpuidle_device *dev)
 	if (!(target->flags & CPUIDLE_FLAG_TIME_VALID))
 		measured_us = USEC_PER_SEC / HZ;
 
+	if ((target->flags & CPUIDLE_FLAG_DEEP) &&
+	    (cpuidle_get_last_residency(dev) < min_deep_sleep)) {
+#if 0
+		printk("F: %d / %d,%d\n", cpuidle_get_last_residency(dev),
+			data->expected_us,data->predicted_us);
+#endif
+		failed_deep++;
+	}
+
 	/* 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);
@@ -102,7 +160,14 @@ static int menu_enable_device(struct cpuidle_device *dev)
 {
 	struct menu_device *data = &per_cpu(menu_devices, dev->cpu);
 
+	printk("Attaching menu governor...\n");
+
 	memset(data, 0, sizeof(struct menu_device));
+	/*
+	 * 0 might be slightly ahead of the current jiffies count, so
+	 * it's a bad initial value.
+	 */
+	data->last_deep = jiffies;
 
 	return 0;
 }
@@ -121,6 +186,8 @@ static struct cpuidle_governor menu_governor = {
  */
 static int __init init_menu(void)
 {
+	global_last_deep = jiffies;
+
 	return cpuidle_register_governor(&menu_governor);
 }
 
@@ -132,6 +199,11 @@ static void __exit exit_menu(void)
 	cpuidle_unregister_governor(&menu_governor);
 }
 
+module_param(min_deep_sleep, uint, 0644)
+MODULE_PARM_DESC(min_deep_sleep, "min time (us) to spend in deep sleep to avoid noise")
+
+module_param(failed_deep, uint, 0644)
+
 MODULE_LICENSE("GPL");
 module_init(init_menu);
 module_exit(exit_menu);


Rgds
-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org
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