[v4,2/2] cpufreq: intel_pstate: Allow raw energy performance preference value
diff mbox series

Message ID 20200626183401.1495090-3-srinivas.pandruvada@linux.intel.com
State Accepted
Commit f473bf398bf1ed42b1bdbc5206a804d8d3140a2d
Headers show
  • cpufreq: intel_pstate: Support raw epp and energy_efficiency
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Commit Message

Srinivas Pandruvada June 26, 2020, 6:34 p.m. UTC
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 are supposed to cover broad spectrum of use cases, but
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
aggressive throttling, which causes a 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 the default "balance_performance" mode can be
aggressive in power consumption. But picking up the next choice
"balance power" results in too much loss of performance, which results in
bad user experience in use cases 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 Chromebook or
for users who wants to fine tune power and performance.
Here based on the product and use cases, different EPP values can be set.
This change is similar to the change done for:
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 present
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(-)


Doug Smythies June 30, 2020, 6:40 p.m. UTC | #1
Hi Srinivas,

Thanks for all your work on this.
I have fallen behind, and not sure when I can catch up.

On 2020.06.26 11:34 Srinivas Pandruvada wrote:

> Similarly on battery the default "balance_performance" mode can be
> aggressive in power consumption. But picking up the next choice
> "balance power" results in too much loss of performance, which results in
> bad user experience in use cases like "Google Hangout". It was observed
> that some value between these two EPP is optimal.

There is a possibility that one of the issues I have been ranting
about could be a contributing factor to things like this.
(I don't know if it actually is.)
One way to compensate is to lower EPP.

I am going to send a new e-mail in a minute about it.
Please consider the possibility that some of these
EPP adjustments might just be programming around the issue.

... Doug

diff mbox series

diff --git a/Documentation/admin-guide/pm/intel_pstate.rst b/Documentation/admin-guide/pm/intel_pstate.rst
index 25e1097fc332..40d481cca368 100644
--- a/Documentation/admin-guide/pm/intel_pstate.rst
+++ b/Documentation/admin-guide/pm/intel_pstate.rst
@@ -565,7 +565,11 @@  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
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 7dfd9da385d1..27737b53dfc6 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -602,11 +602,12 @@  static const unsigned int epp_values[] = {
-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;
 			return 2;
 			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]);