cpuidle: Fix incorrect optimization

fenrus75 · torvalds · commit 1c6fe0364fa7 · 2010-05-09T18:35:36.000-07:00
commit 672917d ("cpuidle: menu governor: reduce latency on exit") added an optimization, where the analysis on the past idle period moved from the end of idle, to the beginning of the new idle. Unfortunately, this optimization had a bug where it zeroed one key variable for new use, that is needed for the analysis. The fix is simple, zero the variable after doing the work from the previous idle. During the audit of the code that found this issue, another issue was also found; the ->measured_us data structure member is never set, a local variable is always used instead. Signed-off-by: Arjan van de Ven <arjan@linux.intel.com> Cc: Corrado Zoccolo <czoccolo@gmail.com> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
@@ -100,7 +100,6 @@ struct menu_device {
 	int             needs_update;
 
 	unsigned int	expected_us;
-	unsigned int	measured_us;
 	u64		predicted_us;
 	unsigned int	exit_us;
 	unsigned int	bucket;
@@ -187,14 +186,14 @@ static int menu_select(struct cpuidle_device *dev)
 	int i;
 	int multiplier;
 
-	data->last_state_idx = 0;
-	data->exit_us = 0;
-
 	if (data->needs_update) {
 		menu_update(dev);
 		data->needs_update = 0;
 	}
 
+	data->last_state_idx = 0;
+	data->exit_us = 0;
+
 	/* Special case when user has set very strict latency requirement */
 	if (unlikely(latency_req == 0))
 		return 0;
@@ -294,7 +293,7 @@ static void menu_update(struct cpuidle_device *dev)
 	new_factor = data->correction_factor[data->bucket]
 			* (DECAY - 1) / DECAY;
 
-	if (data->expected_us > 0 && data->measured_us < MAX_INTERESTING)
+	if (data->expected_us > 0 && measured_us < MAX_INTERESTING)
 		new_factor += RESOLUTION * measured_us / data->expected_us;
 	else
 		/*
