[PATCH 0/7] tools/power x86_energy_perf_policy update

[PATCH 0/7] tools/power x86_energy_perf_policy update

[Len Brown]

Fix a latent bug in the x86_energy_perf_policy utility
that caused confusing results on an upcoming platform.

Please let me know if you have any troubles with it.

thanks,
-Len

[PATCH 1/7] tools/power x86_energy_perf_policy: Enhance HWP enabled check

[Len Brown]

From: Len Brown <len.brown@intel.com>

Verify that all CPUs have HWP enabled, not just cpu0.

Signed-off-by: Len Brown <len.brown@intel.com>
---
 .../x86_energy_perf_policy.c                  | 44 +++++++++++++++----
 1 file changed, 36 insertions(+), 8 deletions(-)

diff --git a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
index ebda9c366b2b..822539a06cfd 100644
--- a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
+++ b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
@@ -4,7 +4,7 @@
  * policy preference bias on recent X86 processors.
  */
 /*
- * Copyright (c) 2010 - 2017 Intel Corporation.
+ * Copyright (c) 2010 - 2025 Intel Corporation.
  * Len Brown <len.brown@intel.com>
  */
 
@@ -517,7 +517,7 @@ void for_packages(unsigned long long pkg_set, int (func)(int))
 
 void print_version(void)
 {
-	printf("x86_energy_perf_policy 17.05.11 (C) Len Brown <len.brown@intel.com>\n");
+	printf("x86_energy_perf_policy 2025.9.19 Len Brown <lenb@kernel.org>\n");
 }
 
 void cmdline(int argc, char **argv)
@@ -1312,6 +1312,17 @@ void for_all_cpus_in_set(size_t set_size, cpu_set_t *cpu_set, int (func)(int))
 		if (CPU_ISSET_S(cpu_num, set_size, cpu_set))
 			func(cpu_num);
 }
+int for_all_cpus_in_set_and(size_t set_size, cpu_set_t *cpu_set, int (func)(int))
+{
+	int cpu_num;
+	int retval = 1;
+
+	for (cpu_num = 0; cpu_num <= max_cpu_num; ++cpu_num)
+		if (CPU_ISSET_S(cpu_num, set_size, cpu_set))
+			retval &= func(cpu_num);
+
+	return retval;
+}
 
 void init_data_structures(void)
 {
@@ -1326,21 +1337,38 @@ void init_data_structures(void)
 	for_all_proc_cpus(mark_cpu_present);
 }
 
-/* clear has_hwp if it is not enable (or being enabled) */
+int is_hwp_enabled_on_cpu(int cpu_num)
+{
+	unsigned long long msr;
+	int retval;
+
+	/* MSR_PM_ENABLE[1] == 1 if HWP is enabled and MSRs visible */
+	get_msr(cpu_num, MSR_PM_ENABLE, &msr);
+	retval = (msr & 1);
 
+	if (verbose)
+		fprintf(stderr, "cpu%d: %sHWP\n", cpu_num, retval ? "" : "No-");
+
+	return retval;
+}
+
+/*
+ * verify_hwp_is_enabled()
+ *
+ * Set (has_hwp=0) if no HWP feature or any of selected CPU set does not have HWP enabled
+ */
 void verify_hwp_is_enabled(void)
 {
-	unsigned long long msr;
+	int retval;
 
 	if (!has_hwp)	/* set in early_cpuid() */
 		return;
 
-	/* MSR_PM_ENABLE[1] == 1 if HWP is enabled and MSRs visible */
-	get_msr(base_cpu, MSR_PM_ENABLE, &msr);
-	if ((msr & 1) == 0) {
+	retval = for_all_cpus_in_set_and(cpu_setsize, cpu_selected_set, is_hwp_enabled_on_cpu);
+
+	if (retval == 0) {
 		fprintf(stderr, "HWP can be enabled using '--hwp-enable'\n");
 		has_hwp = 0;
-		return;
 	}
 }
 
-- 
2.45.2

[PATCH 2/7] tools/power x86_energy_perf_policy: Enhance HWP enable

[Len Brown]

From: Len Brown <len.brown@intel.com>

On enabling HWP, preserve the reserved bits in MSR_PM_ENABLE.

Also, skip writing the MSR_PM_ENABLE if HWP is already enabled.

Signed-off-by: Len Brown <len.brown@intel.com>
---
 .../x86_energy_perf_policy/x86_energy_perf_policy.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
index 822539a06cfd..534e2a70f8ae 100644
--- a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
+++ b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
@@ -1166,13 +1166,18 @@ int update_hwp_request_pkg(int pkg)
 
 int enable_hwp_on_cpu(int cpu)
 {
-	unsigned long long msr;
+	unsigned long long old_msr, new_msr;
+
+	get_msr(cpu, MSR_PM_ENABLE, &old_msr);
+
+	if (old_msr & 1)
+		return 0;	/* already enabled */
 
-	get_msr(cpu, MSR_PM_ENABLE, &msr);
-	put_msr(cpu, MSR_PM_ENABLE, 1);
+	new_msr = old_msr | 1;
+	put_msr(cpu, MSR_PM_ENABLE, new_msr);
 
 	if (verbose)
-		printf("cpu%d: MSR_PM_ENABLE old: %d new: %d\n", cpu, (unsigned int) msr, 1);
+		printf("cpu%d: MSR_PM_ENABLE old: %llX new: %llX\n", cpu, old_msr, new_msr);
 
 	return 0;
 }
-- 
2.45.2

[PATCH 3/7] tools/power x86_energy_perf_policy: Prepare for MSR/sysfs refactoring

[Len Brown]

From: Len Brown <len.brown@intel.com>

Rename routines to make "_msr" and "_sysfs" access  methods clear

No functional change

Signed-off-by: Len Brown <len.brown@intel.com>
---
 .../x86_energy_perf_policy.c                  | 38 +++++++++----------
 1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
index 534e2a70f8ae..47b4efa34a4c 100644
--- a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
+++ b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
@@ -809,7 +809,7 @@ void print_hwp_request_pkg(int pkg, struct msr_hwp_request *h, char *str)
 		h->hwp_min, h->hwp_max, h->hwp_desired, h->hwp_epp,
 		h->hwp_window, h->hwp_window & 0x7F, (h->hwp_window >> 7) & 0x7);
 }
-void read_hwp_request(int cpu, struct msr_hwp_request *hwp_req, unsigned int msr_offset)
+void read_hwp_request_msr(int cpu, struct msr_hwp_request *hwp_req, unsigned int msr_offset)
 {
 	unsigned long long msr;
 
@@ -823,7 +823,7 @@ void read_hwp_request(int cpu, struct msr_hwp_request *hwp_req, unsigned int msr
 	hwp_req->hwp_use_pkg = (((msr) >> 42) & 0x1);
 }
 
-void write_hwp_request(int cpu, struct msr_hwp_request *hwp_req, unsigned int msr_offset)
+void write_hwp_request_msr(int cpu, struct msr_hwp_request *hwp_req, unsigned int msr_offset)
 {
 	unsigned long long msr = 0;
 
@@ -843,7 +843,7 @@ void write_hwp_request(int cpu, struct msr_hwp_request *hwp_req, unsigned int ms
 	put_msr(cpu, msr_offset, msr);
 }
 
-static int get_epb(int cpu)
+static int get_epb_sysfs(int cpu)
 {
 	char path[SYSFS_PATH_MAX];
 	char linebuf[3];
@@ -865,7 +865,7 @@ static int get_epb(int cpu)
 	return (int)val;
 }
 
-static int set_epb(int cpu, int val)
+static int set_epb_sysfs(int cpu, int val)
 {
 	char path[SYSFS_PATH_MAX];
 	char linebuf[3];
@@ -895,14 +895,14 @@ int print_cpu_msrs(int cpu)
 	struct msr_hwp_cap cap;
 	int epb;
 
-	epb = get_epb(cpu);
+	epb = get_epb_sysfs(cpu);
 	if (epb >= 0)
 		printf("cpu%d: EPB %u\n", cpu, (unsigned int) epb);
 
 	if (!has_hwp)
 		return 0;
 
-	read_hwp_request(cpu, &req, MSR_HWP_REQUEST);
+	read_hwp_request_msr(cpu, &req, MSR_HWP_REQUEST);
 	print_hwp_request(cpu, &req, "");
 
 	read_hwp_cap(cpu, &cap, MSR_HWP_CAPABILITIES);
@@ -919,7 +919,7 @@ int print_pkg_msrs(int pkg)
 	if (!has_hwp)
 		return 0;
 
-	read_hwp_request(first_cpu_in_pkg[pkg], &req, MSR_HWP_REQUEST_PKG);
+	read_hwp_request_msr(first_cpu_in_pkg[pkg], &req, MSR_HWP_REQUEST_PKG);
 	print_hwp_request_pkg(pkg, &req, "");
 
 	if (has_hwp_notify) {
@@ -1074,14 +1074,14 @@ int check_hwp_request_v_hwp_capabilities(int cpu, struct msr_hwp_request *req, s
 	return 0;
 }
 
-int update_hwp_request(int cpu)
+int update_hwp_request_msr(int cpu)
 {
 	struct msr_hwp_request req;
 	struct msr_hwp_cap cap;
 
 	int msr_offset = MSR_HWP_REQUEST;
 
-	read_hwp_request(cpu, &req, msr_offset);
+	read_hwp_request_msr(cpu, &req, msr_offset);
 	if (debug)
 		print_hwp_request(cpu, &req, "old: ");
 
@@ -1111,15 +1111,15 @@ int update_hwp_request(int cpu)
 
 	verify_hwp_req_self_consistency(cpu, &req);
 
-	write_hwp_request(cpu, &req, msr_offset);
+	write_hwp_request_msr(cpu, &req, msr_offset);
 
 	if (debug) {
-		read_hwp_request(cpu, &req, msr_offset);
+		read_hwp_request_msr(cpu, &req, msr_offset);
 		print_hwp_request(cpu, &req, "new: ");
 	}
 	return 0;
 }
-int update_hwp_request_pkg(int pkg)
+int update_hwp_request_pkg_msr(int pkg)
 {
 	struct msr_hwp_request req;
 	struct msr_hwp_cap cap;
@@ -1127,7 +1127,7 @@ int update_hwp_request_pkg(int pkg)
 
 	int msr_offset = MSR_HWP_REQUEST_PKG;
 
-	read_hwp_request(cpu, &req, msr_offset);
+	read_hwp_request_msr(cpu, &req, msr_offset);
 	if (debug)
 		print_hwp_request_pkg(pkg, &req, "old: ");
 
@@ -1155,10 +1155,10 @@ int update_hwp_request_pkg(int pkg)
 
 	verify_hwp_req_self_consistency(cpu, &req);
 
-	write_hwp_request(cpu, &req, msr_offset);
+	write_hwp_request_msr(cpu, &req, msr_offset);
 
 	if (debug) {
-		read_hwp_request(cpu, &req, msr_offset);
+		read_hwp_request_msr(cpu, &req, msr_offset);
 		print_hwp_request_pkg(pkg, &req, "new: ");
 	}
 	return 0;
@@ -1188,8 +1188,8 @@ int update_cpu_msrs(int cpu)
 	int epb;
 
 	if (update_epb) {
-		epb = get_epb(cpu);
-		set_epb(cpu, new_epb);
+		epb = get_epb_sysfs(cpu);
+		set_epb_sysfs(cpu, new_epb);
 
 		if (verbose)
 			printf("cpu%d: ENERGY_PERF_BIAS old: %d new: %d\n",
@@ -1229,7 +1229,7 @@ int update_cpu_msrs(int cpu)
 	if (!hwp_update_enabled())
 		return 0;
 
-	update_hwp_request(cpu);
+	update_hwp_request_msr(cpu);
 	return 0;
 }
 
@@ -1587,7 +1587,7 @@ int main(int argc, char **argv)
 		for_all_cpus_in_set(cpu_setsize, cpu_selected_set, update_sysfs);
 		for_all_cpus_in_set(cpu_setsize, cpu_selected_set, update_cpu_msrs);
 	} else if (pkg_selected_set)
-		for_packages(pkg_selected_set, update_hwp_request_pkg);
+		for_packages(pkg_selected_set, update_hwp_request_pkg_msr);
 
 	return 0;
 }
-- 
2.45.2

[PATCH 4/7] tools/power x86_energy_perf_policy: EPB access is only via sysfs

[Len Brown]

From: Len Brown <len.brown@intel.com>

Comprehend that EPB writes are now only via sysfs
by moving it out of the _msr specific path.

No functional change.

Signed-off-by: Len Brown <len.brown@intel.com>
---
 .../x86_energy_perf_policy.c                  | 25 ++++++++++++-------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
index 47b4efa34a4c..0267f5ecaa77 100644
--- a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
+++ b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
@@ -1182,19 +1182,23 @@ int enable_hwp_on_cpu(int cpu)
 	return 0;
 }
 
-int update_cpu_msrs(int cpu)
+int update_cpu_epb_sysfs(int cpu)
 {
-	unsigned long long msr;
 	int epb;
 
-	if (update_epb) {
-		epb = get_epb_sysfs(cpu);
-		set_epb_sysfs(cpu, new_epb);
+	epb = get_epb_sysfs(cpu);
+	set_epb_sysfs(cpu, new_epb);
 
-		if (verbose)
-			printf("cpu%d: ENERGY_PERF_BIAS old: %d new: %d\n",
-				cpu, epb, (unsigned int) new_epb);
-	}
+	if (verbose)
+		printf("cpu%d: ENERGY_PERF_BIAS old: %d new: %d\n",
+			cpu, epb, (unsigned int) new_epb);
+
+	return 0;
+}
+
+int update_cpu_msrs(int cpu)
+{
+	unsigned long long msr;
 
 	if (update_turbo) {
 		int turbo_is_present_and_disabled;
@@ -1584,8 +1588,11 @@ int main(int argc, char **argv)
 
 	/* update CPU set */
 	if (cpu_selected_set) {
+		if (update_epb)
+			for_all_cpus_in_set(cpu_setsize, cpu_selected_set, update_cpu_epb_sysfs);
 		for_all_cpus_in_set(cpu_setsize, cpu_selected_set, update_sysfs);
 		for_all_cpus_in_set(cpu_setsize, cpu_selected_set, update_cpu_msrs);
+
 	} else if (pkg_selected_set)
 		for_packages(pkg_selected_set, update_hwp_request_pkg_msr);
 
-- 
2.45.2

[PATCH 5/7] tools/power x86_energy_perf_policy: Prefer driver HWP limits

[Len Brown]

From: Len Brown <len.brown@intel.com>

When we are successful in using cpufreq min/max limits,
skip setting the raw MSR limits entirely.

This is necessary to avoid undoing any modification that
the cpufreq driver makes to our sysfs request.

eg. intel_pstate may take our request for a limit
that is valid according to HWP.CAP.MIN/MAX and clip
it to be within the range available in PLATFORM_INFO.

Signed-off-by: Len Brown <len.brown@intel.com>
---
 .../x86_energy_perf_policy/x86_energy_perf_policy.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
index 0267f5ecaa77..150cfed95288 100644
--- a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
+++ b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c
@@ -62,6 +62,7 @@ unsigned char turbo_update_value;
 unsigned char update_hwp_epp;
 unsigned char update_hwp_min;
 unsigned char update_hwp_max;
+unsigned char hwp_limits_done_via_sysfs;
 unsigned char update_hwp_desired;
 unsigned char update_hwp_window;
 unsigned char update_hwp_use_pkg;
@@ -951,8 +952,10 @@ int ratio_2_sysfs_khz(int ratio)
 }
 /*
  * If HWP is enabled and cpufreq sysfs attribtes are present,
- * then update sysfs, so that it will not become
- * stale when we write to MSRs.
+ * then update via sysfs. The intel_pstate driver may modify (clip)
+ * this request, say, when HWP_CAP is outside of PLATFORM_INFO limits,
+ * and the driver-chosen value takes precidence.
+ *
  * (intel_pstate's max_perf_pct and min_perf_pct will follow cpufreq,
  *  so we don't have to touch that.)
  */
@@ -1007,6 +1010,8 @@ int update_sysfs(int cpu)
 	if (update_hwp_max)
 		update_cpufreq_scaling_freq(1, cpu, req_update.hwp_max);
 
+	hwp_limits_done_via_sysfs = 1;
+
 	return 0;
 }
 
@@ -1085,10 +1090,10 @@ int update_hwp_request_msr(int cpu)
 	if (debug)
 		print_hwp_request(cpu, &req, "old: ");
 
-	if (update_hwp_min)
+	if (update_hwp_min && !hwp_limits_done_via_sysfs)
 		req.hwp_min = req_update.hwp_min;
 
-	if (update_hwp_max)
+	if (update_hwp_max && !hwp_limits_done_via_sysfs)
 		req.hwp_max = req_update.hwp_max;
 
 	if (update_hwp_desired)
-- 
2.45.2

[PATCH 6/7] tools/power x86_energy_perf_policy: Add make snapshot target

[Len Brown]

From: Len Brown <len.brown@intel.com>

$ make snapshot
creates x86_energy_perf_policy-$(DATE).tar.gz

Which can be transported to a target machine
without needing a kernel tree to build on the target.

Useful for creating debug versions.

Signed-off-by: Len Brown <len.brown@intel.com>
---
 .../power/x86/x86_energy_perf_policy/Makefile | 29 ++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/tools/power/x86/x86_energy_perf_policy/Makefile b/tools/power/x86/x86_energy_perf_policy/Makefile
index 666b325a62a2..d18284667400 100644
--- a/tools/power/x86/x86_energy_perf_policy/Makefile
+++ b/tools/power/x86/x86_energy_perf_policy/Makefile
@@ -1,8 +1,12 @@
 # SPDX-License-Identifier: GPL-2.0
 CC		= $(CROSS_COMPILE)gcc
-BUILD_OUTPUT    := $(CURDIR)
+BUILD_OUTPUT	:= $(CURDIR)
 PREFIX		:= /usr
 DESTDIR		:=
+DAY		:= $(shell date +%Y.%m.%d)
+SNAPSHOT	= x86_energy_perf_policy-$(DAY)
+
+
 
 ifeq ("$(origin O)", "command line")
 	BUILD_OUTPUT := $(O)
@@ -27,3 +31,26 @@ install : x86_energy_perf_policy
 	install -d  $(DESTDIR)$(PREFIX)/share/man/man8
 	install -m 644 x86_energy_perf_policy.8 $(DESTDIR)$(PREFIX)/share/man/man8
 
+snapshot: x86_energy_perf_policy
+	@rm -rf $(SNAPSHOT)
+	@mkdir $(SNAPSHOT)
+	@cp x86_energy_perf_policy Makefile x86_energy_perf_policy.c x86_energy_perf_policy.8 $(SNAPSHOT)
+
+	@sed -e 's/^#include <linux\/bits.h>/#include "bits.h"/' -e 's/u64/unsigned long long/' ../../../../arch/x86/include/asm/msr-index.h > $(SNAPSHOT)/msr-index.h
+	@echo '#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))' >> $(SNAPSHOT)/msr-index.h
+	@echo "#define BIT(x) (1 << (x))" > $(SNAPSHOT)/bits.h
+	@echo "#define BIT_ULL(nr) (1ULL << (nr))" >> $(SNAPSHOT)/bits.h
+	@echo "#define GENMASK(h, l) (((~0UL) << (l)) & (~0UL >> (sizeof(long) * 8 - 1 - (h))))" >> $(SNAPSHOT)/bits.h
+	@echo "#define GENMASK_ULL(h, l) (((~0ULL) << (l)) & (~0ULL >> (sizeof(long long) * 8 - 1 - (h))))" >> $(SNAPSHOT)/bits.h
+
+	@echo '#define BUILD_BUG_ON(cond) do { enum { compile_time_check ## __COUNTER__ = 1/(!(cond)) }; } while (0)' > $(SNAPSHOT)/build_bug.h
+	@echo '#define __must_be_array(arr) 0' >> $(SNAPSHOT)/build_bug.h
+
+	@echo PWD=. > $(SNAPSHOT)/Makefile
+	@echo "CFLAGS +=	-DMSRHEADER='\"msr-index.h\"'" >> $(SNAPSHOT)/Makefile
+	@echo "CFLAGS +=	-DBUILD_BUG_HEADER='\"build_bug.h\"'" >> $(SNAPSHOT)/Makefile
+	@sed -e's/.*MSRHEADER.*//' Makefile >> $(SNAPSHOT)/Makefile
+
+	@rm -f $(SNAPSHOT).tar.gz
+	tar cvzf $(SNAPSHOT).tar.gz $(SNAPSHOT)
+
-- 
2.45.2

[PATCH 7/7] tools/power x86_energy_perf_policy.8: Emphasize preference for SW interfaces

[Len Brown]

From: Len Brown <len.brown@intel.com>

This tool was originally written when Linux had no standard
interface for EPB, or HWP support.

Retain the capability to manage a system w/o any kernel PM support,
but prefer the standard kernel interfaces, when avaialble.

(not doing so led to a confusing conflict between a p-state limit
 request made via cpufreq and modified by the intel-pstate driver,
 versus the raw MSR write made by this utility)

Signed-off-by: Len Brown <len.brown@intel.com>
---
 .../x86_energy_perf_policy.8                      | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.8 b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.8
index 78c6361898b1..0aa981c18e56 100644
--- a/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.8
+++ b/tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.8
@@ -2,7 +2,7 @@
 .\"  Distributed under the GPL, Copyleft 1994.
 .TH X86_ENERGY_PERF_POLICY 8
 .SH NAME
-x86_energy_perf_policy \- Manage Energy vs. Performance Policy via x86 Model Specific Registers
+x86_energy_perf_policy \- Manage Energy vs. Performance Policy
 .SH SYNOPSIS
 .B x86_energy_perf_policy
 .RB "[ options ] [ scope ] [field \ value]"
@@ -19,9 +19,14 @@ x86_energy_perf_policy \- Manage Energy vs. Performance Policy via x86 Model Spe
 .SH DESCRIPTION
 \fBx86_energy_perf_policy\fP
 displays and updates energy-performance policy settings specific to
-Intel Architecture Processors.  Settings are accessed via Model Specific Register (MSR)
-updates, no matter if the Linux cpufreq sub-system is enabled or not.
+Intel Architecture Processors.  It summarizes settings available
+in standard Linux interfaces (eg. cpufreq),
+and also decodes underlying Model Specific Register (MSRs).
+While \fBx86_energy_perf_policy\fP can manage energy-performance policy
+using only MSR access, it prefers standard
+Linux kernel interfaces, when they are available.
 
+.SH BACKGROUND
 Policy in MSR_IA32_ENERGY_PERF_BIAS (EPB)
 may affect a wide range of hardware decisions,
 such as how aggressively the hardware enters and exits CPU idle states (C-states)
@@ -200,7 +205,9 @@ runs only as root.
 .SH FILES
 .ta
 .nf
-/dev/cpu/*/msr
+EPB: /sys/devices/system/cpu/cpu*/power/energy_perf_bias
+EPP: /sys/devices/system/cpu/cpu*/cpufreq/energy_performance_preference
+MSR: /dev/cpu/*/msr
 .fi
 .SH "SEE ALSO"
 .nf
-- 
2.45.2