[PATCH] cpufreq, intel_pstate, set max_sysfs_pct and min_sysfs_pct on governor switch

[Prarit Bhargava <prarit@redhat.com>]

Intel CPUs will not enter higher p-states when after switching from the
performance governor to the powersave governor, until
/sys/devices/system/cpu/intel_pstate/min_perf_pct is set to a low value.
This differs from previous behaviour in which a switch to the powersave
governor would result in a low default value for min_perf_pct.

The behavior of the powersave governor changed after commit a04759924e25
("[cpufreq] intel_pstate: honor user space min_perf_pct override on
resume").  The commit introduced tracking of performance percentage
changes via sysfs in order to restore userspace changes during
suspend/resume.  The problem occurs because the global values of the newly
introduced max_sysfs_pct and min_sysfs_pct are not reset on a governor
change and this causes the new governor to inherit the previous governor's
settings.

This patch sets max_sysfs_pct to 100 and min_sysfs_pct to 0 on a governor
change which fixes the problem with governor switching.  These changes
also make the initial calculations for max_perf_pct and min_perf_pct
slightly simpler.

Before patch:
[root@intel-skylake-y-01 power]# cpupower frequency-set -g performance
[root@intel-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/min_perf_pct
100
[root@intel-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/max_perf_pct
100
[root@intel-skylake-y-01 power]# cpupower frequency-set -g powersave
[root@intel-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/min_perf_pct
100
[root@intel-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/max_perf_pct
100

After patch:
[root@intel-skylake-y-01 power]# cpupower frequency-set -g performance
[root@intel-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/min_perf_pct
100
[root@intel-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/max_perf_pct
100
[root@intel-skylake-y-01 power]# cpupower frequency-set -g powersave
[root@intel-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/min_perf_pct
14
[root@intel-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/max_perf_pct
100

Also note that I have tested suspend/resume (using CONFIG_PM_DEBUG):
[root@intel-skylake-y-01 power]# echo 50 > /sys/devices/system/cpu/intel_pstate/min_perf_pct
[root@intel-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/*_perf_pct
100
50
[root@intel-skylake-y-01 power]# echo devices > /sys/power/pm_test
[root@intel-skylake-y-01 power]# echo platform > /sys/power/disk
[root@intel-skylake-y-01 power]# echo disk > /sys/power/state
[root@intel-skylake-y-01 power]# cat /sys/devices/system/cpu/intel_pstate/*_perf_pct
100
50

Fixes: a04759924e25 ("[cpufreq] intel_pstate: honor user space min_perf_pct override on resume")
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 |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 3af9dd7..bb24458 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -986,6 +986,9 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
 	if (!policy->cpuinfo.max_freq)
 		return -ENODEV;
 
+	limits.min_sysfs_pct = 0;
+	limits.max_sysfs_pct = 100;
+
 	if (policy->policy == CPUFREQ_POLICY_PERFORMANCE &&
 	    policy->max >= policy->cpuinfo.max_freq) {
 		limits.min_policy_pct = 100;
@@ -1004,9 +1007,9 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
 	limits.max_policy_pct = clamp_t(int, limits.max_policy_pct, 0 , 100);
 
 	/* Normalize user input to [min_policy_pct, max_policy_pct] */
-	limits.min_perf_pct = max(limits.min_policy_pct, limits.min_sysfs_pct);
+	limits.min_perf_pct = limits.min_policy_pct;
 	limits.min_perf_pct = min(limits.max_policy_pct, limits.min_perf_pct);
-	limits.max_perf_pct = min(limits.max_policy_pct, limits.max_sysfs_pct);
+	limits.max_perf_pct = limits.max_sysfs_pct;
 	limits.max_perf_pct = max(limits.min_policy_pct, limits.max_perf_pct);
 
 	/* Make sure min_perf_pct <= max_perf_pct */
-- 
1.7.9.3