cpufreq: intel_pstate: Fix ratio setting for min_perf_pct

When the minimum performance limit percentage is set to the power-up
default, it is possible that minimum performance ratio is off by one.

In the set_policy() callback the minimum ratio is calculated by
applying global.min_perf_pct to turbo_ratio and rounding up, but the
power-up default global.min_perf_pct is already rounded up to the
next percent in min_perf_pct_min().  That results in two round up
operations, so for the default min_perf_pct one of them is not
required.

It is better to remove rounding up in min_perf_pct_min() as this
matches the displayed min_perf_pct prior to commit c5a2ee7dde89
(cpufreq: intel_pstate: Active mode P-state limits rework) in 4.12.

For example on a platform with max turbo ratio of 37 and minimum
ratio of 10, the min_perf_pct resulted in 28 with the above commit.
Before this commit it was 27 and it will be the same after this
change.

Fixes: 1a4fe38add8b (cpufreq: intel_pstate: Remove max/min fractions to limit performance)
Reported-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 75648325183275ecc2f3b58809b6ac7b5b0df30b..2386d7036e909c656eef133d1e9854edd2b226cd 100644 (file)
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -572,7 +572,7 @@ static int min_perf_pct_min(void)
        int turbo_pstate = cpu->pstate.turbo_pstate;
 
        return turbo_pstate ?
-               DIV_ROUND_UP(cpu->pstate.min_pstate * 100, turbo_pstate) : 0;
+               (cpu->pstate.min_pstate * 100 / turbo_pstate) : 0;
 }
 
 static s16 intel_pstate_get_epb(struct cpudata *cpu_data)