lib/libsys/getidle.c

   1 /* getidle.c - by David van Moolenbroek <dcvmoole@cs.vu.nl> */
   2
   3 /* Usage:
   4  *
   5  *   double idleperc;
   6  *   getidle();
   7  *   ...
   8  *   idleperc = getidle();
   9  *   if (idleperc >= 0.0)
  10  *     printf("CPU usage: %lg%%\n", 100.0 - idleperc);
  11  *
  12  * Notes:
  13  * - This functionality can only be used by system processes.
  14  * - Only one getidle() run is allowed per process at a time.
  15  *
  16  */
  17
  18 #define _MINIX 1
  19 #define _SYSTEM 1
  20 #include <lib.h>
  21 #include <minix/u64.h>
  22 #include <minix/sysutil.h>
  23 #include <minix/syslib.h>
  24 #include <minix/minlib.h>
  25
  26 static u64_t start, idle;
  27 static int running = 0;
  28
  29 static double make_double(u64_t d)
  30 {
  31 /* Convert a 64-bit fixed point value into a double.
  32  * This whole thing should be replaced by something better eventually.
  33  */
  34   double value;
  35   size_t i;
  36
  37   value = (double) ex64hi(d);
  38   for (i = 0; i < sizeof(unsigned long); i += 2)
  39         value *= 65536.0;
  40
  41   value += (double) ex64lo(d);
  42
  43   return value;
  44 }
  45
  46 double getidle(void)
  47 {
  48   u64_t stop, idle2;
  49   u64_t idelta, tdelta;
  50   double ifp, tfp, rfp;
  51   int r;
  52
  53   if (!running) {
  54         if ((r = sys_getidletsc(&idle)) != OK)
  55                 return -1.0;
  56
  57         running = 1;
  58
  59         read_tsc_64(&start);
  60
  61         return 0.0;
  62   }
  63   else {
  64         read_tsc_64(&stop);
  65
  66         running = 0;
  67
  68         if ((r = sys_getidletsc(&idle2)) != OK)
  69                 return -1.0;
  70
  71         idelta = sub64(idle2, idle);
  72         tdelta = sub64(stop, start);
  73
  74         if (cmp64(idelta, tdelta) >= 0)
  75                 return 100.0;
  76
  77         ifp = make_double(idelta);
  78         tfp = make_double(tdelta);
  79
  80         rfp = ifp / tfp * 100.0;
  81
  82         if (rfp < 0.0) rfp = 0.0;
  83         else if (rfp > 100.0) rfp = 100.0;
  84
  85         return rfp;
  86   }
  87 }