linux-kernel - [PATCH] [26/99] cpuidle: menu: fixed wrapping timers at 4.294 seconds

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Message-Id: <20110727214824.C36E82403FF@tassilo.jf.intel.com>
Date:	Wed, 27 Jul 2011 14:48:24 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	tero.kristo@...ia.com, len.brown@...el.com, gregkh@...e.de,
	ak@...ux.intel.com, linux-kernel@...r.kernel.org,
	stable@...nel.org, tim.bird@...sony.com
Subject: [PATCH] [26/99] cpuidle: menu: fixed wrapping timers at 4.294 seconds

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Tero Kristo <tero.kristo@...ia.com>

commit 7467571f4480b273007517b26297c07154c73924 upstream.

Cpuidle menu governor is using u32 as a temporary datatype for storing
nanosecond values which wrap around at 4.294 seconds. This causes errors
in predicted sleep times resulting in higher than should be C state
selection and increased power consumption. This also breaks cpuidle
state residency statistics.

Signed-off-by: Tero Kristo <tero.kristo@...ia.com>
Signed-off-by: Len Brown <len.brown@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

---
 drivers/cpuidle/governors/menu.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: linux-2.6.35.y/drivers/cpuidle/governors/menu.c
===================================================================
--- linux-2.6.35.y.orig/drivers/cpuidle/governors/menu.c
+++ linux-2.6.35.y/drivers/cpuidle/governors/menu.c
@@ -236,6 +236,7 @@ static int menu_select(struct cpuidle_de
 	int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
 	int i;
 	int multiplier;
+	struct timespec t;
 
 	if (data->needs_update) {
 		menu_update(dev);
@@ -250,8 +251,9 @@ static int menu_select(struct cpuidle_de
 		return 0;
 
 	/* determine the expected residency time, round up */
+	t = ktime_to_timespec(tick_nohz_get_sleep_length());
 	data->expected_us =
-	    DIV_ROUND_UP((u32)ktime_to_ns(tick_nohz_get_sleep_length()), 1000);
+		t.tv_sec * USEC_PER_SEC + t.tv_nsec / NSEC_PER_USEC;
 
 
 	data->bucket = which_bucket(data->expected_us);
--
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