Re: [PATCH] cpufreq: intel_pstate: Fix ratio setting for min_perf_pct

On Monday, July 10, 2017 04:23:52 PM Srinivas Pandruvada wrote:

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

During set_policy() callback the minimum ratio is calculated by applying
global.min_perf_pct to the turbo_ratio and rounding up. But the power-up
default global.min_perf_pct is already rounded up to next percent in the
function min_perf_pct_min(). So this will result in two round up
operations. So for the default min_perf_pct, one of the rounding up 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 the
commit c5a2ee7dde89 ("cpufreq: intel_pstate: Active mode P-state limits
rework") in the kernel version 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 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>

Applied, thanks!