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tools: create power/x86/x86_energy_perf_policy

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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>
This commit is contained in:
Len Brown 2010-10-22 23:53:03 -04:00
parent f6f94e2ab1
commit d5532ee7b4
3 changed files with 437 additions and 0 deletions
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8
tools/power/x86/x86_energy_perf_policy/Makefile Normal file
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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/

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tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.8 Normal file
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.\" 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>

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tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.c Normal file
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/*
* 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;
}