mperf_monitor.c

Go to the documentation of this file.

/*
 *  (C) 2010,2011       Thomas Renninger <[email protected]>, Novell Inc.
 *
 *  Licensed under the terms of the GNU GPL License version 2.
 */

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

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>

#include <cpufreq.h>

#include "helpers/helpers.h"
#include "idle_monitor/cpupower-monitor.h"

#define MSR_APERF   0xE8
#define MSR_MPERF   0xE7

#define MSR_TSC 0x10

#define MSR_AMD_HWCR 0xc0010015

enum mperf_id { C0 = 0, Cx, AVG_FREQ, MPERF_CSTATE_COUNT };

static int mperf_get_count_percent(unsigned int self_id, double *percent,
                   unsigned int cpu);
static int mperf_get_count_freq(unsigned int id, unsigned long long *count,
                unsigned int cpu);
static struct timespec time_start, time_end;

static cstate_t mperf_cstates[MPERF_CSTATE_COUNT] = {
    {
        .name           = "C0",
        .desc           = N_("Processor Core not idle"),
        .id         = C0,
        .range          = RANGE_THREAD,
        .get_count_percent  = mperf_get_count_percent,
    },
    {
        .name           = "Cx",
        .desc           = N_("Processor Core in an idle state"),
        .id         = Cx,
        .range          = RANGE_THREAD,
        .get_count_percent  = mperf_get_count_percent,
    },

    {
        .name           = "Freq",
        .desc           = N_("Average Frequency (including boost) in MHz"),
        .id         = AVG_FREQ,
        .range          = RANGE_THREAD,
        .get_count      = mperf_get_count_freq,
    },
};

enum MAX_FREQ_MODE { MAX_FREQ_SYSFS, MAX_FREQ_TSC_REF };
static int max_freq_mode;
/*
 * The max frequency mperf is ticking at (in C0), either retrieved via:
 *   1) calculated after measurements if we know TSC ticks at mperf/P0 frequency
 *   2) cpufreq /sys/devices/.../cpu0/cpufreq/cpuinfo_max_freq at init time
 * 1. Is preferred as it also works without cpufreq subsystem (e.g. on Xen)
 */
static unsigned long max_frequency;

static unsigned long long tsc_at_measure_start;
static unsigned long long tsc_at_measure_end;
static unsigned long long *mperf_previous_count;
static unsigned long long *aperf_previous_count;
static unsigned long long *mperf_current_count;
static unsigned long long *aperf_current_count;

/* valid flag for all CPUs. If a MSR read failed it will be zero */
static int *is_valid;

static int mperf_get_tsc(unsigned long long *tsc)
{
    int ret;
    ret = read_msr(0, MSR_TSC, tsc);
    if (ret)
        dprint("Reading TSC MSR failed, returning %llu\n", *tsc);
    return ret;
}

static int mperf_init_stats(unsigned int cpu)
{
    unsigned long long val;
    int ret;

    ret = read_msr(cpu, MSR_APERF, &val);
    aperf_previous_count[cpu] = val;
    ret |= read_msr(cpu, MSR_MPERF, &val);
    mperf_previous_count[cpu] = val;
    is_valid[cpu] = !ret;

    return 0;
}

static int mperf_measure_stats(unsigned int cpu)
{
    unsigned long long val;
    int ret;

    ret = read_msr(cpu, MSR_APERF, &val);
    aperf_current_count[cpu] = val;
    ret |= read_msr(cpu, MSR_MPERF, &val);
    mperf_current_count[cpu] = val;
    is_valid[cpu] = !ret;

    return 0;
}

static int mperf_get_count_percent(unsigned int id, double *percent,
                   unsigned int cpu)
{
    unsigned long long aperf_diff, mperf_diff, tsc_diff;
    unsigned long long timediff;

    if (!is_valid[cpu])
        return -1;

    if (id != C0 && id != Cx)
        return -1;

    mperf_diff = mperf_current_count[cpu] - mperf_previous_count[cpu];
    aperf_diff = aperf_current_count[cpu] - aperf_previous_count[cpu];

    if (max_freq_mode == MAX_FREQ_TSC_REF) {
        tsc_diff = tsc_at_measure_end - tsc_at_measure_start;
        *percent = 100.0 * mperf_diff / tsc_diff;
        dprint("%s: TSC Ref - mperf_diff: %llu, tsc_diff: %llu\n",
               mperf_cstates[id].name, mperf_diff, tsc_diff);
    } else if (max_freq_mode == MAX_FREQ_SYSFS) {
        timediff = timespec_diff_us(time_start, time_end);
        *percent = 100.0 * mperf_diff / timediff;
        dprint("%s: MAXFREQ - mperf_diff: %llu, time_diff: %llu\n",
               mperf_cstates[id].name, mperf_diff, timediff);
    } else
        return -1;

    if (id == Cx)
        *percent = 100.0 - *percent;

    dprint("%s: previous: %llu - current: %llu - (%u)\n",
        mperf_cstates[id].name, mperf_diff, aperf_diff, cpu);
    dprint("%s: %f\n", mperf_cstates[id].name, *percent);
    return 0;
}

static int mperf_get_count_freq(unsigned int id, unsigned long long *count,
                unsigned int cpu)
{
    unsigned long long aperf_diff, mperf_diff, time_diff, tsc_diff;

    if (id != AVG_FREQ)
        return 1;

    if (!is_valid[cpu])
        return -1;

    mperf_diff = mperf_current_count[cpu] - mperf_previous_count[cpu];
    aperf_diff = aperf_current_count[cpu] - aperf_previous_count[cpu];

    if (max_freq_mode == MAX_FREQ_TSC_REF) {
        /* Calculate max_freq from TSC count */
        tsc_diff = tsc_at_measure_end - tsc_at_measure_start;
        time_diff = timespec_diff_us(time_start, time_end);
        max_frequency = tsc_diff / time_diff;
    }

    *count = max_frequency * ((double)aperf_diff / mperf_diff);
    dprint("%s: Average freq based on %s maximum frequency:\n",
           mperf_cstates[id].name,
           (max_freq_mode == MAX_FREQ_TSC_REF) ? "TSC calculated" : "sysfs read");
    dprint("%max_frequency: %lu", max_frequency);
    dprint("aperf_diff: %llu\n", aperf_diff);
    dprint("mperf_diff: %llu\n", mperf_diff);
    dprint("avg freq:   %llu\n", *count);
    return 0;
}

static int mperf_start(void)
{
    int cpu;
    unsigned long long dbg;

    clock_gettime(CLOCK_REALTIME, &time_start);
    mperf_get_tsc(&tsc_at_measure_start);

    for (cpu = 0; cpu < cpu_count; cpu++)
        mperf_init_stats(cpu);

    mperf_get_tsc(&dbg);
    dprint("TSC diff: %llu\n", dbg - tsc_at_measure_start);
    return 0;
}

static int mperf_stop(void)
{
    unsigned long long dbg;
    int cpu;

    for (cpu = 0; cpu < cpu_count; cpu++)
        mperf_measure_stats(cpu);

    mperf_get_tsc(&tsc_at_measure_end);
    clock_gettime(CLOCK_REALTIME, &time_end);

    mperf_get_tsc(&dbg);
    dprint("TSC diff: %llu\n", dbg - tsc_at_measure_end);

    return 0;
}

/*
 * Mperf register is defined to tick at P0 (maximum) frequency
 *
 * Instead of reading out P0 which can be tricky to read out from HW,
 * we use TSC counter if it reliably ticks at P0/mperf frequency.
 *
 * Still try to fall back to:
 * /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
 * on older Intel HW without invariant TSC feature.
 * Or on AMD machines where TSC does not tick at P0 (do not exist yet, but
 * it's still double checked (MSR_AMD_HWCR)).
 *
 * On these machines the user would still get useful mperf
 * stats when acpi-cpufreq driver is loaded.
 */
static int init_maxfreq_mode(void)
{
    int ret;
    unsigned long long hwcr;
    unsigned long min;

    if (!cpupower_cpu_info.caps & CPUPOWER_CAP_INV_TSC)
        goto use_sysfs;

    if (cpupower_cpu_info.vendor == X86_VENDOR_AMD) {
        /* MSR_AMD_HWCR tells us whether TSC runs at P0/mperf
         * freq.
         * A test whether hwcr is accessable/available would be:
         * (cpupower_cpu_info.family > 0x10 ||
         *   cpupower_cpu_info.family == 0x10 &&
         *   cpupower_cpu_info.model >= 0x2))
         * This should be the case for all aperf/mperf
         * capable AMD machines and is therefore safe to test here.
         * Compare with Linus kernel git commit: acf01734b1747b1ec4
         */
        ret = read_msr(0, MSR_AMD_HWCR, &hwcr);
        /*
         * If the MSR read failed, assume a Xen system that did
         * not explicitly provide access to it and assume TSC works
        */
        if (ret != 0) {
            dprint("TSC read 0x%x failed - assume TSC working\n",
                   MSR_AMD_HWCR);
            return 0;
        } else if (1 & (hwcr >> 24)) {
            max_freq_mode = MAX_FREQ_TSC_REF;
            return 0;
        } else { /* Use sysfs max frequency if available */ }
    } else if (cpupower_cpu_info.vendor == X86_VENDOR_INTEL) {
        /*
         * On Intel we assume mperf (in C0) is ticking at same
         * rate than TSC
         */
        max_freq_mode = MAX_FREQ_TSC_REF;
        return 0;
    }
use_sysfs:
    if (cpufreq_get_hardware_limits(0, &min, &max_frequency)) {
        dprint("Cannot retrieve max freq from cpufreq kernel "
               "subsystem\n");
        return -1;
    }
    max_freq_mode = MAX_FREQ_SYSFS;
    return 0;
}

/*
 * This monitor provides:
 *
 * 1) Average frequency a CPU resided in
 *    This always works if the CPU has aperf/mperf capabilities
 *
 * 2) C0 and Cx (any sleep state) time a CPU resided in
 *    Works if mperf timer stops ticking in sleep states which
 *    seem to be the case on all current HW.
 * Both is directly retrieved from HW registers and is independent
 * from kernel statistics.
 */
struct cpuidle_monitor mperf_monitor;
struct cpuidle_monitor *mperf_register(void)
{
    if (!(cpupower_cpu_info.caps & CPUPOWER_CAP_APERF))
        return NULL;

    if (init_maxfreq_mode())
        return NULL;

    /* Free this at program termination */
    is_valid = calloc(cpu_count, sizeof(int));
    mperf_previous_count = calloc(cpu_count, sizeof(unsigned long long));
    aperf_previous_count = calloc(cpu_count, sizeof(unsigned long long));
    mperf_current_count = calloc(cpu_count, sizeof(unsigned long long));
    aperf_current_count = calloc(cpu_count, sizeof(unsigned long long));

    mperf_monitor.name_len = strlen(mperf_monitor.name);
    return &mperf_monitor;
}

void mperf_unregister(void)
{
    free(mperf_previous_count);
    free(aperf_previous_count);
    free(mperf_current_count);
    free(aperf_current_count);
    free(is_valid);
}

struct cpuidle_monitor mperf_monitor = {
    .name           = "Mperf",
    .hw_states_num      = MPERF_CSTATE_COUNT,
    .hw_states      = mperf_cstates,
    .start          = mperf_start,
    .stop           = mperf_stop,
    .do_register        = mperf_register,
    .unregister     = mperf_unregister,
    .needs_root     = 1,
    .overflow_s     = 922000000 /* 922337203 seconds TSC overflow
                           at 20GHz */
};
#endif /* #if defined(__i386__) || defined(__x86_64__) */