linux-kernel - [PATCH 1/2] cpufreq, intel_pstate, Fix limits->max_policy

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Date:	Fri, 20 Nov 2015 07:32:36 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Prarit Bhargava <prarit@...hat.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...el.com>,
	Len Brown <len.brown@...el.com>,
	Alexandra Yates <alexandra.yates@...el.com>,
	Kristen Carlson Accardi <kristen@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-pm@...r.kernel.org
Subject: [PATCH 1/2] cpufreq, intel_pstate, Fix limits->max_policy_pct rounding error

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@...el.com>
Cc: Len Brown <len.brown@...el.com>
Cc: Alexandra Yates <alexandra.yates@...el.com>
Cc: Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Cc: linux-pm@...r.kernel.org
Signed-off-by: Prarit Bhargava <prarit@...hat.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

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