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