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  *   printf("CPU usage: %lg%%\n", 100.0 - idleperc);
  10  *
  11  * This routine goes through PM to get the idle time, rather than making the
  12  * sys_getinfo() call to the kernel directly. This means that it can be used
  13  * by non-system processes as well, but it will incur some extra overhead in
  14  * the system case. The overhead does not end up being measured, because the
  15  * system is clearly not idle while the system calls are being made. In any
  16  * case, for this reason, only one getidle() run is allowed at a time.
  17  *
  18  * Note that the kernel has to be compiled with CONFIG_IDLE_TSC support.
  19  */
  20
  21 #define _MINIX 1
  22 #define _SYSTEM 1
  23 #include <minix/sysinfo.h>
  24 #include <minix/u64.h>
  25 #include <minix/sysutil.h>
  26
  27 static u64_t start, idle;
  28 static int running = 0;
  29
  30 static double make_double(u64_t d)
  31 {
  32 /* Convert a 64-bit fixed point value into a double.
  33  * This whole thing should be replaced by something better eventually.
  34  */
  35   double value;
  36   size_t i;
  37
  38   value = (double) ex64hi(d);
  39   for (i = 0; i < sizeof(unsigned long); i += 2)
  40         value *= 65536.0;
  41
  42   value += (double) ex64lo(d);
  43
  44   return value;
  45 }
  46
  47 double getidle(void)
  48 {
  49   u64_t stop, idle2;
  50   u64_t idelta, tdelta;
  51   double ifp, tfp, rfp;
  52   int r;
  53
  54   if (!running) {
  55         r = getsysinfo_up(PM_PROC_NR, SIU_IDLETSC, sizeof(idle), &idle);
  56         if (r != sizeof(idle))
  57                 return -1.0;
  58
  59         running = 1;
  60
  61         read_tsc_64(&start);
  62
  63         return 0.0;
  64   }
  65   else {
  66         read_tsc_64(&stop);
  67
  68         running = 0;
  69
  70         r = getsysinfo_up(PM_PROC_NR, SIU_IDLETSC, sizeof(idle2), &idle2);
  71         if (r != sizeof(idle2))
  72                 return -1.0;
  73
  74         idelta = sub64(idle2, idle);
  75         tdelta = sub64(stop, start);
  76
  77         if (cmp64(idelta, tdelta) >= 0)
  78                 return 100.0;
  79
  80         ifp = make_double(idelta);
  81         tfp = make_double(tdelta);
  82
  83         rfp = ifp / tfp * 100.0;
  84
  85         if (rfp < 0.0) rfp = 0.0;
  86         else if (rfp > 100.0) rfp = 100.0;
  87
  88         return rfp;
  89   }
  90
  91   running = !running;
  92 }