diff mbox

cpuidle: poll_state: Add time limit to poll_idle()

Message ID 6734090.QOs8nIFVJO@aspire.rjw.lan (mailing list archive)
State Superseded, archived
Headers show

Commit Message

Rafael J. Wysocki March 11, 2018, 10:15 a.m. UTC 
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

If poll_idle() is allowed to spin until need_resched() returns 'true',
it may actually spin for a much longer time than expected by the idle
governor, since set_tsk_need_resched() is not always called by the
timer interrupt handler.  If that happens, the CPU may spend much
more time than anticipated in the "polling" state.

To prevent that from happening, limit the time of the spinning loop
in poll_idle().

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/cpuidle/poll_state.c |   17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)
diff mbox

Patch

Index: linux-pm/drivers/cpuidle/poll_state.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/poll_state.c
+++ linux-pm/drivers/cpuidle/poll_state.c
@@ -5,16 +5,31 @@ 
  */
 
 #include <linux/cpuidle.h>
+#include <linux/ktime.h>
 #include <linux/sched.h>
 #include <linux/sched/idle.h>
 
+#define POLL_IDLE_TIME_CHECK_COUNT	10000
+#define POLL_IDLE_TIME_LIMIT		(TICK_NSEC / 16)
+
 static int __cpuidle poll_idle(struct cpuidle_device *dev,
 			       struct cpuidle_driver *drv, int index)
 {
+	ktime_t start = ktime_get();
+
 	local_irq_enable();
 	if (!current_set_polling_and_test()) {
-		while (!need_resched())
+		unsigned int time_check_counter = 0;
+
+		while (!need_resched()) {
 			cpu_relax();
+			if (time_check_counter++ < POLL_IDLE_TIME_CHECK_COUNT)
+				continue;
+
+			time_check_counter = 0;
+			if (ktime_sub(ktime_get(), start) > POLL_IDLE_TIME_LIMIT)
+				break;
+		}
 	}
 	current_clr_polling();