@@ -561,7 +561,11 @@ somewhere between the two extremes:
Strings written to the ``energy_performance_preference`` attribute are
internally translated to integer values written to the processor's
Energy-Performance Preference (EPP) knob (if supported) or its
-Energy-Performance Bias (EPB) knob.
+Energy-Performance Bias (EPB) knob. It is also possible to write a positive
+integer value between 0 to 255, if the EPP feature is present. If the EPP
+feature is not present, writing integer value to this attribute is not
+supported. In this case, user can use
+ "/sys/devices/system/cpu/cpu*/power/energy_perf_bias" interface.
[Note that tasks may by migrated from one CPU to another by the scheduler's
load-balancing algorithm and if different energy vs performance hints are
@@ -602,11 +602,12 @@ static const unsigned int epp_values[] = {
HWP_EPP_POWERSAVE
};
-static int intel_pstate_get_energy_pref_index(struct cpudata *cpu_data)
+static int intel_pstate_get_energy_pref_index(struct cpudata *cpu_data, int *raw_epp)
{
s16 epp;
int index = -EINVAL;
+ *raw_epp = 0;
epp = intel_pstate_get_epp(cpu_data, 0);
if (epp < 0)
return epp;
@@ -614,12 +615,14 @@ static int intel_pstate_get_energy_pref_index(struct cpudata *cpu_data)
if (boot_cpu_has(X86_FEATURE_HWP_EPP)) {
if (epp == HWP_EPP_PERFORMANCE)
return 1;
- if (epp <= HWP_EPP_BALANCE_PERFORMANCE)
+ if (epp == HWP_EPP_BALANCE_PERFORMANCE)
return 2;
- if (epp <= HWP_EPP_BALANCE_POWERSAVE)
+ if (epp == HWP_EPP_BALANCE_POWERSAVE)
return 3;
- else
+ if (epp == HWP_EPP_POWERSAVE)
return 4;
+ *raw_epp = epp;
+ return 0;
} else if (boot_cpu_has(X86_FEATURE_EPB)) {
/*
* Range:
@@ -638,7 +641,8 @@ static int intel_pstate_get_energy_pref_index(struct cpudata *cpu_data)
}
static int intel_pstate_set_energy_pref_index(struct cpudata *cpu_data,
- int pref_index)
+ int pref_index, bool use_raw,
+ u32 raw_epp)
{
int epp = -EINVAL;
int ret;
@@ -657,6 +661,16 @@ static int intel_pstate_set_energy_pref_index(struct cpudata *cpu_data,
value &= ~GENMASK_ULL(31, 24);
+ if (use_raw) {
+ if (raw_epp > 255) {
+ ret = -EINVAL;
+ goto return_pref;
+ }
+ value |= (u64)raw_epp << 24;
+ ret = wrmsrl_on_cpu(cpu_data->cpu, MSR_HWP_REQUEST, value);
+ goto return_pref;
+ }
+
if (epp == -EINVAL)
epp = epp_values[pref_index - 1];
@@ -694,6 +708,8 @@ static ssize_t store_energy_performance_preference(
{
struct cpudata *cpu_data = all_cpu_data[policy->cpu];
char str_preference[21];
+ bool raw = false;
+ u32 epp;
int ret;
ret = sscanf(buf, "%20s", str_preference);
@@ -701,10 +717,21 @@ static ssize_t store_energy_performance_preference(
return -EINVAL;
ret = match_string(energy_perf_strings, -1, str_preference);
- if (ret < 0)
+ if (ret < 0) {
+ if (!boot_cpu_has(X86_FEATURE_HWP_EPP))
+ return ret;
+
+ ret = kstrtouint(buf, 10, &epp);
+ if (ret)
+ return ret;
+
+ raw = true;
+ }
+
+ ret = intel_pstate_set_energy_pref_index(cpu_data, ret, raw, epp);
+ if (ret)
return ret;
- intel_pstate_set_energy_pref_index(cpu_data, ret);
return count;
}
@@ -712,13 +739,16 @@ static ssize_t show_energy_performance_preference(
struct cpufreq_policy *policy, char *buf)
{
struct cpudata *cpu_data = all_cpu_data[policy->cpu];
- int preference;
+ int preference, raw_epp;
- preference = intel_pstate_get_energy_pref_index(cpu_data);
+ preference = intel_pstate_get_energy_pref_index(cpu_data, &raw_epp);
if (preference < 0)
return preference;
- return sprintf(buf, "%s\n", energy_perf_strings[preference]);
+ if (raw_epp)
+ return sprintf(buf, "%d\n", raw_epp);
+ else
+ return sprintf(buf, "%s\n", energy_perf_strings[preference]);
}
cpufreq_freq_attr_rw(energy_performance_preference);
Currently using attribute "energy_performance_preference", user space can write one of the four per-defined preference string. These preference strings gets mapped to a hard-coded Energy-Performance Preference (EPP) or Energy-Performance Bias (EPB) knob. These four values supposed to cover broad spectrum of use cases, but they are not uniformly distributed in the range. There are number of cases, where this is not enough. For example: Suppose user wants more performance when connected to AC. Instead of using default "balance performance", the "performance" setting can be used. This changes EPP value from 0x80 to 0x00. But setting EPP to 0, results in electrical and thermal issues on some platforms. This results in CPU to do aggressive throttling, which causes drop in performance. But some value between 0x80 and 0x00 results in better performance. But that value can't be fixed as the power curve is not linear. In some cases just changing EPP from 0x80 to 0x75 is enough to get significant performance gain. Similarly on battery EPP 0x80 can be very aggressive in power consumption. But picking up the next choice "balance power" results in too much loss of performance, which cause bad user experience in use case like "Google Hangout". It was observed that some value between these two EPP is optimal. This change allows fine grain EPP tuning for platform like Chromebooks. Here based on the product and use cases, different EPP values can be set. This change is similar to the change done for: /sys/devices/system/cpu/cpu*/power/energy_perf_bias where user has choice to write a predefined string or raw value. The change itself is trivial. When user preference doesn't match predefined string preferences and value is an unsigned integer and in range, use that value for EPP. When the EPP feature is not prsent writing raw value is not supported. Suggested-by: Len Brown <lenb@kernel.org> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> --- Documentation/admin-guide/pm/intel_pstate.rst | 6 ++- drivers/cpufreq/intel_pstate.c | 50 +++++++++++++++---- 2 files changed, 45 insertions(+), 11 deletions(-)