msr.c

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#if defined(__i386__) || defined(__x86_64__)

#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdint.h>

#include "helpers/helpers.h"

/* Intel specific MSRs */
#define MSR_IA32_PERF_STATUS        0x198
#define MSR_IA32_MISC_ENABLES       0x1a0
#define MSR_IA32_ENERGY_PERF_BIAS   0x1b0
#define MSR_NEHALEM_TURBO_RATIO_LIMIT   0x1ad

/*
 * read_msr
 *
 * Will return 0 on success and -1 on failure.
 * Possible errno values could be:
 * EFAULT -If the read/write did not fully complete
 * EIO    -If the CPU does not support MSRs
 * ENXIO  -If the CPU does not exist
 */

int read_msr(int cpu, unsigned int idx, unsigned long long *val)
{
    int fd;
    char msr_file_name[64];

    sprintf(msr_file_name, "/dev/cpu/%d/msr", cpu);
    fd = open(msr_file_name, O_RDONLY);
    if (fd < 0)
        return -1;
    if (lseek(fd, idx, SEEK_CUR) == -1)
        goto err;
    if (read(fd, val, sizeof *val) != sizeof *val)
        goto err;
    close(fd);
    return 0;
 err:
    close(fd);
    return -1;
}

/*
 * write_msr
 *
 * Will return 0 on success and -1 on failure.
 * Possible errno values could be:
 * EFAULT -If the read/write did not fully complete
 * EIO    -If the CPU does not support MSRs
 * ENXIO  -If the CPU does not exist
 */
int write_msr(int cpu, unsigned int idx, unsigned long long val)
{
    int fd;
    char msr_file_name[64];

    sprintf(msr_file_name, "/dev/cpu/%d/msr", cpu);
    fd = open(msr_file_name, O_WRONLY);
    if (fd < 0)
        return -1;
    if (lseek(fd, idx, SEEK_CUR) == -1)
        goto err;
    if (write(fd, &val, sizeof val) != sizeof val)
        goto err;
    close(fd);
    return 0;
 err:
    close(fd);
    return -1;
}

int msr_intel_get_perf_bias(unsigned int cpu)
{
    unsigned long long val;
    int ret;

    if (!(cpupower_cpu_info.caps & CPUPOWER_CAP_PERF_BIAS))
        return -1;

    ret = read_msr(cpu, MSR_IA32_ENERGY_PERF_BIAS, &val);
    if (ret)
        return ret;
    return val;
}

int msr_intel_set_perf_bias(unsigned int cpu, unsigned int val)
{
    int ret;

    if (!(cpupower_cpu_info.caps & CPUPOWER_CAP_PERF_BIAS))
        return -1;

    ret = write_msr(cpu, MSR_IA32_ENERGY_PERF_BIAS, val);
    if (ret)
        return ret;
    return 0;
}

unsigned long long msr_intel_get_turbo_ratio(unsigned int cpu)
{
    unsigned long long val;
    int ret;

    if (!(cpupower_cpu_info.caps & CPUPOWER_CAP_HAS_TURBO_RATIO))
        return -1;

    ret = read_msr(cpu, MSR_NEHALEM_TURBO_RATIO_LIMIT, &val);
    if (ret)
        return ret;
    return val;
}
#endif