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

Viresh Kumar
2015-11-20T13:18:39Z

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 ? :)

--
viresh