linux-kernel - [PATCH] Resolve time unit thinko in ondemand/conservative govs

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Date:	Wed, 11 Nov 2009 16:50:29 -0800
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Dave Jones <davej@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	Alexander Miller <Miller@....uni-stuttgart.de>
Subject: [PATCH] Resolve time unit thinko in ondemand/conservative govs


Dave,

Here is the fix for the bug reported on this thread. Please Apply. Looks to
be a stable candidate as well.

Thanks,
Venki

ondemand and conservative governors are messing up time units in the
code path where NO_HZ is not enabled and ignore_nice is set. The walltime
idletime stored is in jiffies and nice time calculation is happening in
microseconds.

The problem was reported and diagnosed by Alexander here.
http://marc.info/?l=linux-kernel&m=125752550404513&w=2

The patch below fixes this thinko.

Reported-by: Alexander Miller <Miller@....uni-stuttgart.de>
Tested-by: Alexander Miller <Miller@....uni-stuttgart.de>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
---
 drivers/cpufreq/cpufreq_conservative.c |    4 ++--
 drivers/cpufreq/cpufreq_ondemand.c     |    4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
index bc33ddc..c7b081b 100644
--- a/drivers/cpufreq/cpufreq_conservative.c
+++ b/drivers/cpufreq/cpufreq_conservative.c
@@ -116,9 +116,9 @@ static inline cputime64_t get_cpu_idle_time_jiffy(unsigned int cpu,
 
 	idle_time = cputime64_sub(cur_wall_time, busy_time);
 	if (wall)
-		*wall = cur_wall_time;
+		*wall = (cputime64_t)jiffies_to_usecs(cur_wall_time);
 
-	return idle_time;
+	return (cputime64_t)jiffies_to_usecs(idle_time);;
 }
 
 static inline cputime64_t get_cpu_idle_time(unsigned int cpu, cputime64_t *wall)
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index 071699d..4b34ade 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -133,9 +133,9 @@ static inline cputime64_t get_cpu_idle_time_jiffy(unsigned int cpu,
 
 	idle_time = cputime64_sub(cur_wall_time, busy_time);
 	if (wall)
-		*wall = cur_wall_time;
+		*wall = (cputime64_t)jiffies_to_usecs(cur_wall_time);
 
-	return idle_time;
+	return (cputime64_t)jiffies_to_usecs(idle_time);
 }
 
 static inline cputime64_t get_cpu_idle_time(unsigned int cpu, cputime64_t *wall)
-- 
1.6.0.6

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