This is a note to let you know that I've just added the patch titled
cpufreq: Fix wrong time unit conversion
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cpufreq-fix-wrong-time-unit-conversion.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From a857c0b9e24e39fe5be82451b65377795f9538d8 Mon Sep 17 00:00:00 2001
From: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
Date: Sat, 7 Sep 2013 18:35:08 +0200
Subject: cpufreq: Fix wrong time unit conversion
From: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
commit a857c0b9e24e39fe5be82451b65377795f9538d8 upstream.
The time spent by a CPU under a given frequency is stored in jiffies unit
in the cpu var cpufreq_stats_table->time_in_state[i], i being the index of
the frequency.
This is what is displayed in the following file on the right column:
cat /sys/devices/system/cpu/cpuX/cpufreq/stats/time_in_state
2301000 19835820
2300000 3172
[...]
Now cpufreq converts this jiffies unit delta to clock_t before returning it
to the user as in the above file. And that conversion is achieved using the API
cputime64_to_clock_t().
Although it accidentally works on traditional tick based cputime accounting, where
cputime_t maps directly to jiffies, it doesn't work with other types of cputime
accounting such as CONFIG_VIRT_CPU_ACCOUNTING_* where cputime_t can map to nsecs
or any granularity preffered by the architecture.
For example we get a buggy zero delta on full dyntick configurations:
cat /sys/devices/system/cpu/cpuX/cpufreq/stats/time_in_state
2301000 0
2300000 0
[...]
Fix this with using the proper jiffies_64_t to clock_t conversion.
Reported-and-tested-by: Carsten Emde <C.Emde@xxxxxxxxx>
Signed-off-by: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/cpufreq/cpufreq_stats.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/cpufreq/cpufreq_stats.c
+++ b/drivers/cpufreq/cpufreq_stats.c
@@ -81,7 +81,7 @@ static ssize_t show_time_in_state(struct
for (i = 0; i < stat->state_num; i++) {
len += sprintf(buf + len, "%u %llu\n", stat->freq_table[i],
(unsigned long long)
- cputime64_to_clock_t(stat->time_in_state[i]));
+ jiffies_64_to_clock_t(stat->time_in_state[i]));
}
return len;
}
Patches currently in stable-queue which might be from schwab@xxxxxxxxxxxxxx are
queue-3.10/cpufreq-fix-wrong-time-unit-conversion.patch
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