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

Prarit Bhargava
2015-11-20T12:32:44Z

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;
limits->max_policy_pct = clamp_t(int, limits->max_policy_pct, 0 , 100);
+ 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,
--
1.8.3.1