tools: create power/x86/x86_energy_perf_policy

MSR_IA32_ENERGY_PERF_BIAS first became available on Westmere Xeon.
It is implemented in all Sandy Bridge processors -- mobile, desktop and server.
It is expected to become increasingly important in subsequent generations.

x86_energy_perf_policy is a user-space utility to set the
hardware energy vs performance policy hint in the processor.
Most systems would benefit from "x86_energy_perf_policy normal"
at system startup, as the hardware default is maximum performance
at the expense of energy efficiency.

See x86_energy_perf_policy.8 man page for more information.

Background:

Linux-2.6.36 added "epb" to /proc/cpuinfo to indicate
if an x86 processor supports MSR_IA32_ENERGY_PERF_BIAS,
without actually modifying the MSR.

In March, 2010, Venkatesh Pallipadi proposed a small driver
that programmed MSR_IA32_ENERGY_PERF_BIAS, based on
the cpufreq governor in use.  It also offered
a boot-time cmdline option to override.
http://lkml.org/lkml/2010/3/4/457
But hiding the hardware policy behind the
governor choice was deemed "kinda icky".

In June, 2010, I proposed a generic user/kernel API to
generalize the power/performance policy trade-off.
"RFC: /sys/power/policy_preference"
http://lkml.org/lkml/2010/6/16/399
That is my preference for implementing this capability,
but I received no support on the list.

So in September, 2010, I sent x86_energy_perf_policy.c to LKML,
a user-space utility that scribbles directly to the MSR.
http://lkml.org/lkml/2010/9/28/246

Here is that same utility, after responding to some review feedback,
to live in tools/power/, where it is easily found.
Signed-off-by: Len Brown <len.brown@intel.com>

tools/power/x86/x86_energy_perf_policy/Makefile

+x86_energy_perf_policy : x86_energy_perf_policy.c
+
+clean :
+	rm -f x86_energy_perf_policy
+
+install :
+	install x86_energy_perf_policy /usr/bin/
+	install x86_energy_perf_policy.8 /usr/share/man/man8/

tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.8

+.\"  This page Copyright (C) 2010 Len Brown <len.brown@intel.com>
+.\"  Distributed under the GPL, Copyleft 1994.
+.TH X86_ENERGY_PERF_POLICY 8
+.SH NAME
+x86_energy_perf_policy \- read or write MSR_IA32_ENERGY_PERF_BIAS
+.SH SYNOPSIS
+.ft B
+.B x86_energy_perf_policy
+.RB [ "\-c cpu" ]
+.RB [ "\-v" ]
+.RB "\-r"
+.br
+.B x86_energy_perf_policy
+.RB [ "\-c cpu" ]
+.RB [ "\-v" ]
+.RB 'performance'
+.br
+.B x86_energy_perf_policy
+.RB [ "\-c cpu" ]
+.RB [ "\-v" ]
+.RB 'normal'
+.br
+.B x86_energy_perf_policy
+.RB [ "\-c cpu" ]
+.RB [ "\-v" ]
+.RB 'powersave'
+.br
+.B x86_energy_perf_policy
+.RB [ "\-c cpu" ]
+.RB [ "\-v" ]
+.RB n
+.br
+.SH DESCRIPTION
+\fBx86_energy_perf_policy\fP
+allows software to convey
+its policy for the relative importance of performance
+versus energy savings to the processor.
+
+The processor uses this information in model-specific ways
+when it must select trade-offs between performance and
+energy efficiency.
+
+This policy hint does not supersede Processor Performance states
+(P-states) or CPU Idle power states (C-states), but allows
+software to have influence where it would otherwise be unable
+to express a preference.
+
+For example, this setting may tell the hardware how
+aggressively or conservatively to control frequency
+in the "turbo range" above the explicitly OS-controlled
+P-state frequency range.  It may also tell the hardware
+how aggressively is should enter the OS requested C-states.
+
+Support for this feature is indicated by CPUID.06H.ECX.bit3
+per the Intel Architectures Software Developer's Manual.
+
+.SS Options
+\fB-c\fP limits operation to a single CPU.
+The default is to operate on all CPUs.
+Note that MSR_IA32_ENERGY_PERF_BIAS is defined per
+logical processor, but that the initial implementations
+of the MSR were shared among all processors in each package.
+.PP
+\fB-v\fP increases verbosity.  By default
+x86_energy_perf_policy is silent.
+.PP
+\fB-r\fP is for "read-only" mode - the unchanged state
+is read and displayed.
+.PP
+.I performance
+Set a policy where performance is paramount.
+The processor will be unwilling to sacrifice any performance
+for the sake of energy saving. This is the hardware default.
+.PP
+.I normal
+Set a policy with a normal balance between performance and energy efficiency.
+The processor will tolerate minor performance compromise
+for potentially significant energy savings.
+This reasonable default for most desktops and servers.
+.PP
+.I powersave
+Set a policy where the processor can accept
+a measurable performance hit to maximize energy efficiency.
+.PP
+.I n
+Set MSR_IA32_ENERGY_PERF_BIAS to the specified number.
+The range of valid numbers is 0-15, where 0 is maximum
+performance and 15 is maximum energy efficiency.
+
+.SH NOTES
+.B "x86_energy_perf_policy "
+runs only as root.
+.SH FILES
+.ta
+.nf
+/dev/cpu/*/msr
+.fi
+
+.SH "SEE ALSO"
+msr(4)
+.PP
+.SH AUTHORS
+.nf
+Written by Len Brown <len.brown@intel.com>

tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c

+/*
+ * x86_energy_perf_policy -- set the energy versus performance
+ * policy preference bias on recent X86 processors.
+ */
+/*
+ * Copyright (c) 2010, Intel Corporation.
+ * Len Brown <len.brown@intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/resource.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <sys/time.h>
+#include <stdlib.h>
+#include <string.h>
+
+unsigned int verbose;		/* set with -v */
+unsigned int read_only;		/* set with -r */
+char *progname;
+unsigned long long new_bias;
+int cpu = -1;
+
+/*
+ * Usage:
+ *
+ * -c cpu: limit action to a single CPU (default is all CPUs)
+ * -v: verbose output (can invoke more than once)
+ * -r: read-only, don't change any settings
+ *
+ *  performance
+ *	Performance is paramount.
+ *	Unwilling to sacrafice any performance
+ *	for the sake of energy saving. (hardware default)
+ *
+ *  normal
+ *	Can tolerate minor performance compromise
+ *	for potentially significant energy savings.
+ *	(reasonable default for most desktops and servers)
+ *
+ *  powersave
+ *	Can tolerate significant performance hit
+ *	to maximize energy savings.
+ *
+ * n
+ *	a numerical value to write to the underlying MSR.
+ */
+void usage(void)
+{
+	printf("%s: [-c cpu] [-v] "
+		"(-r | 'performance' | 'normal' | 'powersave' | n)\n",
+		progname);
+	exit(1);
+}
+
+#define MSR_IA32_ENERGY_PERF_BIAS	0x000001b0
+
+#define	BIAS_PERFORMANCE		0
+#define BIAS_BALANCE			6
+#define	BIAS_POWERSAVE			15
+
+void cmdline(int argc, char **argv)
+{
+	int opt;
+
+	progname = argv[0];
+
+	while ((opt = getopt(argc, argv, "+rvc:")) != -1) {
+		switch (opt) {
+		case 'c':
+			cpu = atoi(optarg);
+			break;
+		case 'r':
+			read_only = 1;
+			break;
+		case 'v':
+			verbose++;
+			break;
+		default:
+			usage();
+		}
+	}
+	/* if -r, then should be no additional optind */
+	if (read_only && (argc > optind))
+		usage();
+
+	/*
+	 * if no -r , then must be one additional optind
+	 */
+	if (!read_only) {
+
+		if (argc != optind + 1) {
+			printf("must supply -r or policy param\n");
+			usage();
+			}
+
+		if (!strcmp("performance", argv[optind])) {
+			new_bias = BIAS_PERFORMANCE;
+		} else if (!strcmp("normal", argv[optind])) {
+			new_bias = BIAS_BALANCE;
+		} else if (!strcmp("powersave", argv[optind])) {
+			new_bias = BIAS_POWERSAVE;
+		} else {
+			char *endptr;
+
+			new_bias = strtoull(argv[optind], &endptr, 0);
+			if (endptr == argv[optind] ||
+				new_bias > BIAS_POWERSAVE) {
+					fprintf(stderr, "invalid value: %s\n",
+						argv[optind]);
+				usage();
+			}
+		}
+	}
+}
+
+/*
+ * validate_cpuid()
+ * returns on success, quietly exits on failure (make verbose with -v)
+ */
+void validate_cpuid(void)
+{
+	unsigned int eax, ebx, ecx, edx, max_level;
+	char brand[16];
+	unsigned int fms, family, model, stepping;
+
+	eax = ebx = ecx = edx = 0;
+
+	asm("cpuid" : "=a" (max_level), "=b" (ebx), "=c" (ecx),
+		"=d" (edx) : "a" (0));
+
+	if (ebx != 0x756e6547 || edx != 0x49656e69 || ecx != 0x6c65746e) {
+		if (verbose)
+			fprintf(stderr, "%.4s%.4s%.4s != GenuineIntel",
+				(char *)&ebx, (char *)&edx, (char *)&ecx);
+		exit(1);
+	}
+
+	asm("cpuid" : "=a" (fms), "=c" (ecx), "=d" (edx) : "a" (1) : "ebx");
+	family = (fms >> 8) & 0xf;
+	model = (fms >> 4) & 0xf;
+	stepping = fms & 0xf;
+	if (family == 6 || family == 0xf)
+		model += ((fms >> 16) & 0xf) << 4;
+
+	if (verbose > 1)
+		printf("CPUID %s %d levels family:model:stepping "
+			"0x%x:%x:%x (%d:%d:%d)\n", brand, max_level,
+			family, model, stepping, family, model, stepping);
+
+	if (!(edx & (1 << 5))) {
+		if (verbose)
+			printf("CPUID: no MSR\n");
+		exit(1);
+	}
+
+	/*
+	 * Support for MSR_IA32_ENERGY_PERF_BIAS
+	 * is indicated by CPUID.06H.ECX.bit3
+	 */
+	asm("cpuid" : "=a" (eax), "=b" (ebx), "=c" (ecx), "=d" (edx) : "a" (6));
+	if (verbose)
+		printf("CPUID.06H.ECX: 0x%x\n", ecx);
+	if (!(ecx & (1 << 3))) {
+		if (verbose)
+			printf("CPUID: No MSR_IA32_ENERGY_PERF_BIAS\n");
+		exit(1);
+	}
+	return;	/* success */
+}
+
+unsigned long long get_msr(int cpu, int offset)
+{
+	unsigned long long msr;
+	char msr_path[32];
+	int retval;
+	int fd;
+
+	sprintf(msr_path, "/dev/cpu/%d/msr", cpu);
+	fd = open(msr_path, O_RDONLY);
+	if (fd < 0) {
+		printf("Try \"# modprobe msr\"\n");
+		perror(msr_path);
+		exit(1);
+	}
+
+	retval = pread(fd, &msr, sizeof msr, offset);
+
+	if (retval != sizeof msr) {
+		printf("pread cpu%d 0x%x = %d\n", cpu, offset, retval);
+		exit(-2);
+	}
+	close(fd);
+	return msr;
+}
+
+unsigned long long  put_msr(int cpu, unsigned long long new_msr, int offset)
+{
+	unsigned long long old_msr;
+	char msr_path[32];
+	int retval;
+	int fd;
+
+	sprintf(msr_path, "/dev/cpu/%d/msr", cpu);
+	fd = open(msr_path, O_RDWR);
+	if (fd < 0) {
+		perror(msr_path);
+		exit(1);
+	}
+
+	retval = pread(fd, &old_msr, sizeof old_msr, offset);
+	if (retval != sizeof old_msr) {
+		perror("pwrite");
+		printf("pread cpu%d 0x%x = %d\n", cpu, offset, retval);
+		exit(-2);
+	}
+
+	retval = pwrite(fd, &new_msr, sizeof new_msr, offset);
+	if (retval != sizeof new_msr) {
+		perror("pwrite");
+		printf("pwrite cpu%d 0x%x = %d\n", cpu, offset, retval);
+		exit(-2);
+	}
+
+	close(fd);
+
+	return old_msr;
+}
+
+void print_msr(int cpu)
+{
+	printf("cpu%d: 0x%016llx\n",
+		cpu, get_msr(cpu, MSR_IA32_ENERGY_PERF_BIAS));
+}
+
+void update_msr(int cpu)
+{
+	unsigned long long previous_msr;
+
+	previous_msr = put_msr(cpu, new_bias, MSR_IA32_ENERGY_PERF_BIAS);
+
+	if (verbose)
+		printf("cpu%d  msr0x%x 0x%016llx -> 0x%016llx\n",
+			cpu, MSR_IA32_ENERGY_PERF_BIAS, previous_msr, new_bias);
+
+	return;
+}
+
+char *proc_stat = "/proc/stat";
+/*
+ * run func() on every cpu in /dev/cpu
+ */
+void for_every_cpu(void (func)(int))
+{
+	FILE *fp;
+	int retval;
+
+	fp = fopen(proc_stat, "r");
+	if (fp == NULL) {
+		perror(proc_stat);
+		exit(1);
+	}
+
+	retval = fscanf(fp, "cpu %*d %*d %*d %*d %*d %*d %*d %*d %*d %*d\n");
+	if (retval != 0) {
+		perror("/proc/stat format");
+		exit(1);
+	}
+
+	while (1) {
+		int cpu;
+
+		retval = fscanf(fp,
+			"cpu%u %*d %*d %*d %*d %*d %*d %*d %*d %*d %*d\n",
+			&cpu);
+		if (retval != 1)
+			return;
+
+		func(cpu);
+	}
+	fclose(fp);
+}
+
+int main(int argc, char **argv)
+{
+	cmdline(argc, argv);
+
+	if (verbose > 1)
+		printf("x86_energy_perf_policy Nov 24, 2010"
+				" - Len Brown <lenb@kernel.org>\n");
+	if (verbose > 1 && !read_only)
+		printf("new_bias %lld\n", new_bias);
+
+	validate_cpuid();
+
+	if (cpu != -1) {
+		if (read_only)
+			print_msr(cpu);
+		else
+			update_msr(cpu);
+	} else {
+		if (read_only)
+			for_every_cpu(print_msr);
+		else
+			for_every_cpu(update_msr);
+	}
+
+	return 0;
+}