Re: [PATCH 3/6] cpufreq: tolerate inexact values when collecting stats

MyungJoo Ham
2012-11-01T02:14:21Z

On Wed, Oct 31, 2012 at 9:03 PM, Mark Langsdorf
<mark.langsdorf@calxeda.com> wrote:
> Allow frequency values to vary by +/-5000 Hz when collecting stats.
>
> Signed-off-by: Mark Langsdorf <mark.langsdorf@calxeda.com>
> Cc: cpufreq@vger.kernel.org
> Cc: Rafael J. Wysocki <rjw@sisk.pl>

If we are getting values with some variations from policy->cur and we
can sure that the every "intended" frequency is already included in
the freq_table[] array, why don't we simply do rounding based on the
freq_table[]? (choosing the closest value from the table)

Besides, your proposal may incur bugs in my system (look at the first
two values):

mzx@hisui:~/test$ cat
/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
3401000 3400000 3200000 3000000 2800000 2600000 2400000 2200000
2000000 1800000 1600000
mzx@hisui:~/test$ cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 42
model name : Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz
stepping : 7
cpu MHz : 1600.000
cache size : 8192 KB
[skip]

Cheers,
MyungJoo

>
> ---
> drivers/cpufreq/cpufreq_stats.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
> index 3998316..4e2ea7e 100644
> --- a/drivers/cpufreq/cpufreq_stats.c
> +++ b/drivers/cpufreq/cpufreq_stats.c
> @@ -158,9 +158,11 @@ static struct attribute_group stats_attr_group = {
> static int freq_table_get_index(struct cpufreq_stats *stat, unsigned int freq)
> {
> int index;
> - for (index = 0; index < stat->max_state; index++)
> - if (stat->freq_table[index] == freq)
> + for (index = 0; index < stat->max_state; index++) {
> + if ((stat->freq_table[index] < (freq + 5000)) &&
> + (stat->freq_table[index] > (freq - 5000)))
> return index;
> + }
> return -1;
> }
>
> @@ -251,6 +253,8 @@ static int cpufreq_stats_create_table(struct cpufreq_policy *policy,
> spin_lock(&cpufreq_stats_lock);
> stat->last_time = get_jiffies_64();
> stat->last_index = freq_table_get_index(stat, policy->cur);
> + if (stat->last_index > stat->max_state)
> + stat->last_index = stat->max_state - 1;
> spin_unlock(&cpufreq_stats_lock);
> cpufreq_cpu_put(data);
> return 0;
> --
> 1.7.11.7
>
> --
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--
MyungJoo Ham, Ph.D.
System S/W Lab, S/W Center, Samsung Electronics