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 <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Viresh Kumar <[email protected]>
Cc: [email protected]
Signed-off-by: Prarit Bhargava <[email protected]>
---
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
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