On Saturday, September 07, 2013 12:02:26 PM Paul E. McKenney wrote:
> On Sat, Sep 07, 2013 at 06:35:08PM +0200, Frederic Weisbecker wrote:
> > 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-by: Carsten Emde <[email protected]>
> > Tested-by: Carsten Emde <[email protected]>
> > Signed-off-by: Frederic Weisbecker <[email protected]>
> > Cc: Carsten Emde <[email protected]>
> > Cc: Thomas Gleixner <[email protected]>
> > Cc: Clark Williams <[email protected]>
> > Cc: Sebastian Andrzej Siewior <[email protected]>
> > Cc: Paul E. McKenney <[email protected]>
>
> Good catch!
>
> Acked-by: Paul E. McKenney <[email protected]>
Applied, will push for 3.12-rc1.
Thanks Frederic!
>
> > ---
> > drivers/cpufreq/cpufreq_stats.c | 2 +-
> > 1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/drivers/cpufreq/cpufreq_stats.c
> > b/drivers/cpufreq/cpufreq_stats.c
> > index d37568c..10e6138 100644
> > --- a/drivers/cpufreq/cpufreq_stats.c
> > +++ b/drivers/cpufreq/cpufreq_stats.c
> > @@ -81,7 +81,7 @@ static ssize_t show_time_in_state(struct cpufreq_policy
> > *policy, char *buf)
> > 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;
> > }
>
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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