cpufreq: AMD "frequency sensitivity feedback" powersave bias for ondemand governor

Future AMD processors, starting with Family 16h, can provide software
with feedback on how the workload may respond to frequency change --
memory-bound workloads will not benefit from higher frequency, where
as compute-bound workloads will. This patch enables this "frequency
sensitivity feedback" to aid the ondemand governor to make better
frequency change decisions by hooking into the powersave bias.

Signed-off-by: Jacob Shin <[e-mail]>
Acked-by: Thomas Renninger <[e-mail]>
Acked-by: Borislav Petkov <[e-mail]>
Acked-by: Viresh Kumar <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

Documentation/cpu-freq/governors.txt

···
 busy, rather than shifting back and forth in speed. This tunable has no
 effect on behavior at lower speeds/lower CPU loads.
 
+powersave_bias: this parameter takes a value between 0 to 1000. It
+defines the percentage (times 10) value of the target frequency that
+will be shaved off of the target. For example, when set to 100 -- 10%,
+when ondemand governor would have targeted 1000 MHz, it will target
+1000 MHz - (10% of 1000 MHz) = 900 MHz instead. This is set to 0
+(disabled) by default.
+When AMD frequency sensitivity powersave bias driver --
+drivers/cpufreq/amd_freq_sensitivity.c is loaded, this parameter
+defines the workload frequency sensitivity threshold in which a lower
+frequency is chosen instead of ondemand governor's original target.
+The frequency sensitivity is a hardware reported (on AMD Family 16h
+Processors and above) value between 0 to 100% that tells software how
+the performance of the workload running on a CPU will change when
+frequency changes. A workload with sensitivity of 0% (memory/IO-bound)
+will not perform any better on higher core frequency, whereas a
+workload with sensitivity of 100% (CPU-bound) will perform better
+higher the frequency. When the driver is loaded, this is set to 400
+by default -- for CPUs running workloads with sensitivity value below
+40%, a lower frequency is chosen. Unloading the driver or writing 0
+will disable this feature.
+
 
 2.5 Conservative
 ----------------

arch/x86/include/asm/cpufeature.h

···
 #define X86_FEATURE_PTS		(7*32+ 6) /* Intel Package Thermal Status */
 #define X86_FEATURE_DTHERM	(7*32+ 7) /* Digital Thermal Sensor */
 #define X86_FEATURE_HW_PSTATE	(7*32+ 8) /* AMD HW-PState */
+#define X86_FEATURE_PROC_FEEDBACK (7*32+ 9) /* AMD ProcFeedbackInterface */
 
 /* Virtualization flags: Linux defined, word 8 */
 #define X86_FEATURE_TPR_SHADOW  (8*32+ 0) /* Intel TPR Shadow */

arch/x86/kernel/cpu/scattered.c

···
 		{ X86_FEATURE_APERFMPERF,	CR_ECX, 0, 0x00000006, 0 },
 		{ X86_FEATURE_EPB,		CR_ECX, 3, 0x00000006, 0 },
 		{ X86_FEATURE_XSAVEOPT,		CR_EAX,	0, 0x0000000d, 1 },
-		{ X86_FEATURE_CPB,		CR_EDX, 9, 0x80000007, 0 },
 		{ X86_FEATURE_HW_PSTATE,	CR_EDX, 7, 0x80000007, 0 },
+		{ X86_FEATURE_CPB,		CR_EDX, 9, 0x80000007, 0 },
+		{ X86_FEATURE_PROC_FEEDBACK,	CR_EDX,11, 0x80000007, 0 },
 		{ X86_FEATURE_NPT,		CR_EDX, 0, 0x8000000a, 0 },
 		{ X86_FEATURE_LBRV,		CR_EDX, 1, 0x8000000a, 0 },
 		{ X86_FEATURE_SVML,		CR_EDX, 2, 0x8000000a, 0 },

drivers/cpufreq/Kconfig.x86

···
 
 	  For details, take a look at <file:Documentation/cpu-freq/>.
 
+config X86_AMD_FREQ_SENSITIVITY
+	tristate "AMD frequency sensitivity feedback powersave bias"
+	depends on CPU_FREQ_GOV_ONDEMAND && X86_ACPI_CPUFREQ && CPU_SUP_AMD
+	help
+	  This adds AMD-specific powersave bias function to the ondemand
+	  governor, which allows it to make more power-conscious frequency
+	  change decisions based on feedback from hardware (availble on AMD
+	  Family 16h and above).
+
+	  Hardware feedback tells software how "sensitive" to frequency changes
+	  the CPUs' workloads are. CPU-bound workloads will be more sensitive
+	  -- they will perform better as frequency increases. Memory/IO-bound
+	  workloads will be less sensitive -- they will not necessarily perform
+	  better as frequency increases.
+
+	  If in doubt, say N.
+
 config X86_GX_SUSPMOD
 	tristate "Cyrix MediaGX/NatSemi Geode Suspend Modulation"
 	depends on X86_32 && PCI

drivers/cpufreq/Makefile

···
 obj-$(CONFIG_X86_P4_CLOCKMOD)		+= p4-clockmod.o
 obj-$(CONFIG_X86_CPUFREQ_NFORCE2)	+= cpufreq-nforce2.o
 obj-$(CONFIG_X86_INTEL_PSTATE)		+= intel_pstate.o
+obj-$(CONFIG_X86_AMD_FREQ_SENSITIVITY)	+= amd_freq_sensitivity.o
 
 ##################################################################################
 # ARM SoC drivers

drivers/cpufreq/amd_freq_sensitivity.c

···
+/*
+ * amd_freq_sensitivity.c: AMD frequency sensitivity feedback powersave bias
+ *                         for the ondemand governor.
+ *
+ * Copyright (C) 2013 Advanced Micro Devices, Inc.
+ *
+ * Author: Jacob Shin <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/percpu-defs.h>
+#include <linux/init.h>
+#include <linux/mod_devicetable.h>
+
+#include <asm/msr.h>
+#include <asm/cpufeature.h>
+
+#include "cpufreq_governor.h"
+
+#define MSR_AMD64_FREQ_SENSITIVITY_ACTUAL	0xc0010080
+#define MSR_AMD64_FREQ_SENSITIVITY_REFERENCE	0xc0010081
+#define CLASS_CODE_SHIFT			56
+#define POWERSAVE_BIAS_MAX			1000
+#define POWERSAVE_BIAS_DEF			400
+
+struct cpu_data_t {
+	u64 actual;
+	u64 reference;
+	unsigned int freq_prev;
+};
+
+static DEFINE_PER_CPU(struct cpu_data_t, cpu_data);
+
+static unsigned int amd_powersave_bias_target(struct cpufreq_policy *policy,
+					      unsigned int freq_next,
+					      unsigned int relation)
+{
+	int sensitivity;
+	long d_actual, d_reference;
+	struct msr actual, reference;
+	struct cpu_data_t *data = &per_cpu(cpu_data, policy->cpu);
+	struct dbs_data *od_data = policy->governor_data;
+	struct od_dbs_tuners *od_tuners = od_data->tuners;
+	struct od_cpu_dbs_info_s *od_info =
+		od_data->cdata->get_cpu_dbs_info_s(policy->cpu);
+
+	if (!od_info->freq_table)
+		return freq_next;
+
+	rdmsr_on_cpu(policy->cpu, MSR_AMD64_FREQ_SENSITIVITY_ACTUAL,
+		&actual.l, &actual.h);
+	rdmsr_on_cpu(policy->cpu, MSR_AMD64_FREQ_SENSITIVITY_REFERENCE,
+		&reference.l, &reference.h);
+	actual.h &= 0x00ffffff;
+	reference.h &= 0x00ffffff;
+
+	/* counter wrapped around, so stay on current frequency */
+	if (actual.q < data->actual || reference.q < data->reference) {
+		freq_next = policy->cur;
+		goto out;
+	}
+
+	d_actual = actual.q - data->actual;
+	d_reference = reference.q - data->reference;
+
+	/* divide by 0, so stay on current frequency as well */
+	if (d_reference == 0) {
+		freq_next = policy->cur;
+		goto out;
+	}
+
+	sensitivity = POWERSAVE_BIAS_MAX -
+		(POWERSAVE_BIAS_MAX * (d_reference - d_actual) / d_reference);
+
+	clamp(sensitivity, 0, POWERSAVE_BIAS_MAX);
+
+	/* this workload is not CPU bound, so choose a lower freq */
+	if (sensitivity < od_tuners->powersave_bias) {
+		if (data->freq_prev == policy->cur)
+			freq_next = policy->cur;
+
+		if (freq_next > policy->cur)
+			freq_next = policy->cur;
+		else if (freq_next < policy->cur)
+			freq_next = policy->min;
+		else {
+			unsigned int index;
+
+			cpufreq_frequency_table_target(policy,
+				od_info->freq_table, policy->cur - 1,
+				CPUFREQ_RELATION_H, &index);
+			freq_next = od_info->freq_table[index].frequency;
+		}
+
+		data->freq_prev = freq_next;
+	} else
+		data->freq_prev = 0;
+
+out:
+	data->actual = actual.q;
+	data->reference = reference.q;
+	return freq_next;
+}
+
+static int __init amd_freq_sensitivity_init(void)
+{
+	u64 val;
+
+	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
+		return -ENODEV;
+
+	if (!static_cpu_has(X86_FEATURE_PROC_FEEDBACK))
+		return -ENODEV;
+
+	if (rdmsrl_safe(MSR_AMD64_FREQ_SENSITIVITY_ACTUAL, &val))
+		return -ENODEV;
+
+	if (!(val >> CLASS_CODE_SHIFT))
+		return -ENODEV;
+
+	od_register_powersave_bias_handler(amd_powersave_bias_target,
+			POWERSAVE_BIAS_DEF);
+	return 0;
+}
+late_initcall(amd_freq_sensitivity_init);
+
+static void __exit amd_freq_sensitivity_exit(void)
+{
+	od_unregister_powersave_bias_handler();
+}
+module_exit(amd_freq_sensitivity_exit);
+
+static const struct x86_cpu_id amd_freq_sensitivity_ids[] = {
+	X86_FEATURE_MATCH(X86_FEATURE_PROC_FEEDBACK),
+	{}
+};
+MODULE_DEVICE_TABLE(x86cpu, amd_freq_sensitivity_ids);
+
+MODULE_AUTHOR("Jacob Shin <[e-mail]>");
+MODULE_DESCRIPTION("AMD frequency sensitivity feedback powersave bias for "
+		"the ondemand governor.");
+MODULE_LICENSE("GPL");