include/asm-i386/tsc.h

   1 /*
   2  * linux/include/asm-i386/tsc.h
   3  *
   4  * i386 TSC related functions
   5  */
   6 #ifndef _ASM_i386_TSC_H
   7 #define _ASM_i386_TSC_H
   8
   9 #include <asm/processor.h>
  10
  11 /*
  12  * Standard way to access the cycle counter on i586+ CPUs.
  13  * Currently only used on SMP.
  14  *
  15  * If you really have a SMP machine with i486 chips or older,
  16  * compile for that, and this will just always return zero.
  17  * That's ok, it just means that the nicer scheduling heuristics
  18  * won't work for you.
  19  *
  20  * We only use the low 32 bits, and we'd simply better make sure
  21  * that we reschedule before that wraps. Scheduling at least every
  22  * four billion cycles just basically sounds like a good idea,
  23  * regardless of how fast the machine is.
  24  */
  25 typedef unsigned long long cycles_t;
  26
  27 extern unsigned int cpu_khz;
  28 extern unsigned int tsc_khz;
  29
  30 static inline cycles_t get_cycles(void)
  31 {
  32         unsigned long long ret = 0;
  33
  34 #ifndef CONFIG_X86_TSC
  35         if (!cpu_has_tsc)
  36                 return 0;
  37 #endif
  38
  39 #if defined(CONFIG_X86_GENERIC) || defined(CONFIG_X86_TSC)
  40         rdtscll(ret);
  41 #endif
  42         return ret;
  43 }
  44
  45 extern void tsc_init(void);
  46 extern void mark_tsc_unstable(void);
  47
  48 #endif