get_clock.c

/*
 * Copyright (c) 2005 Mellanox Technologies Ltd.  All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - Redistributions in binary form must reproduce the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer in the documentation and/or other materials
 *        provided with the distribution.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 * $Id$
 *
 * Author: Michael S. Tsirkin <mst@mellanox.co.il>
 */

/* #define DEBUG 1 */
/* #define DEBUG_DATA 1 */
/* #define GET_CPU_MHZ_FROM_PROC 1 */

/* For gettimeofday */
#define _DEFAULT_SOURCE
#include <sys/time.h>

#include <unistd.h>
#include <stdio.h>
#include "get_clock.h"

#ifndef DEBUG
#define DEBUG 0
#endif
#ifndef DEBUG_DATA
#define DEBUG_DATA 0
#endif

#define MEASUREMENTS 200
#define USECSTEP 10
#define USECSTART 100

/*
 Use linear regression to calculate cycles per microsecond.
 http://en.wikipedia.org/wiki/Linear_regression#Parameter_estimation
*/
static double sample_get_cpu_mhz(void) {
  struct timeval tv1, tv2;
  cycles_t start;
  double sx = 0, sy = 0, sxx = 0, syy = 0, sxy = 0;
  double tx, ty;
  int i;

  /* Regression: y = a + b x */
  long x[MEASUREMENTS];
  cycles_t y[MEASUREMENTS];
  double a; /* system call overhead in cycles */
  double b; /* cycles per microsecond */
  double r_2;

  for (i = 0; i < MEASUREMENTS; ++i) {
    start = get_cycles();

    if (gettimeofday(&tv1, NULL)) {
      fprintf(stderr, "gettimeofday failed.\n");
      return 0;
    }

    do {
      if (gettimeofday(&tv2, NULL)) {
        fprintf(stderr, "gettimeofday failed.\n");
        return 0;
      }
    }
    while ((tv2.tv_sec - tv1.tv_sec) * 1000000 +
           (tv2.tv_usec - tv1.tv_usec) < USECSTART + i * USECSTEP);

    x[i] = (tv2.tv_sec - tv1.tv_sec) * 1000000 +
           tv2.tv_usec - tv1.tv_usec;
    y[i] = get_cycles() - start;
    if (DEBUG_DATA)
      fprintf(stderr, "x=%ld y=%Ld\n", x[i], (long long)y[i]);
  }

  for (i = 0; i < MEASUREMENTS; ++i) {
    tx = x[i];
    ty = y[i];
    sx += tx;
    sy += ty;
    sxx += tx * tx;
    syy += ty * ty;
    sxy += tx * ty;
  }

  b = (MEASUREMENTS * sxy - sx * sy) / (MEASUREMENTS * sxx - sx * sx);
  a = (sy - b * sx) / MEASUREMENTS;

  if (DEBUG)
    fprintf(stderr, "a = %g\n", a);
  if (DEBUG)
    fprintf(stderr, "b = %g\n", b);
  if (DEBUG)
    fprintf(stderr, "a / b = %g\n", a / b);
  r_2 = (MEASUREMENTS * sxy - sx * sy) * (MEASUREMENTS * sxy - sx * sy) /
        (MEASUREMENTS * sxx - sx * sx) /
        (MEASUREMENTS * syy - sy * sy);

  if (DEBUG)
    fprintf(stderr, "r^2 = %g\n", r_2);
  if (r_2 < 0.9) {
    fprintf(stderr,"Correlation coefficient r^2: %g < 0.9\n", r_2);
    return 0;
  }

  return b;
}

static double proc_get_cpu_mhz(int no_cpu_freq_fail) {
  FILE* f;
  char buf[256];
  double mhz = 0.0;

  f = fopen("/proc/cpuinfo","r");
  if (!f)
    return 0.0;
  while(fgets(buf, sizeof(buf), f)) {
    double m;
    int rc;

#if defined (__ia64__)
    /* Use the ITC frequency on IA64 */
    rc = sscanf(buf, "itc MHz : %lf", &m);
#elif defined (__PPC__) || defined (__PPC64__)
    /* PPC has a different format as well */
    rc = sscanf(buf, "clock : %lf", &m);
#else
    rc = sscanf(buf, "cpu MHz : %lf", &m);
#endif

    if (rc != 1)
      continue;

    if (mhz == 0.0) {
      mhz = m;
      continue;
    }
    if (mhz != m) {
      fprintf(stderr, "Conflicting CPU frequency values"
              " detected: %lf != %lf\n", mhz, m);
      if (no_cpu_freq_fail) {
        fprintf(stderr, "Test integrity may be harmed !\n");
      }
      else {
        return 0.0;
      }
      continue;
    }
  }
  fclose(f);
  return mhz;
}


double get_cpu_mhz(int no_cpu_freq_fail) {
  double sample, proc, delta;
  sample = sample_get_cpu_mhz();
  proc = proc_get_cpu_mhz(no_cpu_freq_fail);

  if (!proc || !sample)
    return 0;

  delta = proc > sample ? proc - sample : sample - proc;
  if (delta / proc > 0.01) {
    fprintf(stderr, "Warning: measured timestamp frequency "
            "%g differs from nominal %g MHz\n",
            sample, proc);
    return sample;
  }
  return proc;
}