Re: [PATCH 1/2] cpufreq, intel_pstate, Fix limits->max_policy_pct rounding error

Prarit Bhargava
2015-11-20T15:10:05Z

On 11/20/2015 08:18 AM, Viresh Kumar wrote:
> On 20-11-15, 07:32, Prarit Bhargava wrote:
>> I have a Intel (6,63) processor with a "marketing" frequency (from
>> /proc/cpuinfo) of 2100MHz, and a max turbo frequency of 2600MHz. I
>> can execute
>>
>> cpupower frequency-set -g powersave --min 1200MHz --max 2100MHz
>>
>> and the max_freq_pct is set to 80. When adding load to the system I noticed
>> that the cpu frequency only reached 2000MHZ and not 2100MHz as expected.
>>
>> This is because limits->max_policy_pct is calculated as 2100 * 100 /2600 = 80.7
>> and is rounded down to 80 when it should be rounded up to 81. This patch
>> adds a DIV_ROUND_UP() which will return the correct value.
>>
>> Cc: Srinivas Pandruvada <srinivas.pandruvada@intel.com>
>> Cc: Len Brown <len.brown@intel.com>
>> Cc: Alexandra Yates <alexandra.yates@intel.com>
>> Cc: Kristen Carlson Accardi <kristen@linux.intel.com>
>> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
>> Cc: Viresh Kumar <viresh.kumar@linaro.org>
>> Cc: linux-pm@vger.kernel.org
>> Signed-off-by: Prarit Bhargava <prarit@redhat.com>
>> ---
>> drivers/cpufreq/intel_pstate.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
>> index 001a532..6b63374 100644
>> --- a/drivers/cpufreq/intel_pstate.c
>> +++ b/drivers/cpufreq/intel_pstate.c
>> @@ -1110,6 +1110,8 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
>> limits->min_policy_pct = clamp_t(int, limits->min_policy_pct, 0 , 100);
>> limits->max_policy_pct = (policy->max * 100) / policy->cpuinfo.max_freq;
>
> Forgot to remove this line ?
>
>> limits->max_policy_pct = clamp_t(int, limits->max_policy_pct, 0 , 100);
>
> And put this after the later one ?
>
>> + limits->max_policy_pct = DIV_ROUND_UP(policy->max * 100,
>> + policy->cpuinfo.max_freq);
>>
>> /* Normalize user input to [min_policy_pct, max_policy_pct] */
>> limits->min_perf_pct = max(limits->min_policy_pct,
>
> Sure you tested it ? :)

Oops -- and yeah, tested. It works because I rewrite the value of
max_policy_pct :). I'll repost shortly.

P.

>