cpufreq: Fix wrong time unit conversion
authorAndreas Schwab <schwab@linux-m68k.org>
Sat, 7 Sep 2013 16:35:08 +0000 (18:35 +0200)
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>
Tue, 10 Sep 2013 00:49:46 +0000 (02:49 +0200)
commita857c0b9e24e39fe5be82451b65377795f9538d8
tree9a1338d24be24c358b2fb00e4cfcc2a5fa6b5b6a
parent19c763031acb831a5ab9c1a701b7fedda073eb3f
cpufreq: Fix wrong time unit conversion

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@osadl.org>
Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
drivers/cpufreq/cpufreq_stats.c