include/asm-x86/tsc.h

   1 /*
   2  * x86 TSC related functions
   3  */
   4 #ifndef _ASM_X86_TSC_H
   5 #define _ASM_X86_TSC_H
   6
   7 #include <asm/processor.h>
   8
   9 #define NS_SCALE        10 /* 2^10, carefully chosen */
  10 #define US_SCALE        32 /* 2^32, arbitralrily chosen */
  11
  12 /*
  13  * Standard way to access the cycle counter.
  14  */
  15 typedef unsigned long long cycles_t;
  16
  17 extern unsigned int cpu_khz;
  18 extern unsigned int tsc_khz;
  19
  20 static inline cycles_t get_cycles(void)
  21 {
  22         unsigned long long ret = 0;
  23
  24 #ifndef CONFIG_X86_TSC
  25         if (!cpu_has_tsc)
  26                 return 0;
  27 #endif
  28
  29 #if defined(CONFIG_X86_GENERIC) || defined(CONFIG_X86_TSC)
  30         rdtscll(ret);
  31 #endif
  32         return ret;
  33 }
  34
  35 /* Like get_cycles, but make sure the CPU is synchronized. */
  36 static __always_inline cycles_t __get_cycles_sync(void)
  37 {
  38         unsigned long long ret;
  39         unsigned eax, edx;
  40
  41         /*
  42          * Use RDTSCP if possible; it is guaranteed to be synchronous
  43          * and doesn't cause a VMEXIT on Hypervisors
  44          */
  45         alternative_io(ASM_NOP3, ".byte 0x0f,0x01,0xf9", X86_FEATURE_RDTSCP,
  46                        ASM_OUTPUT2("=a" (eax), "=d" (edx)),
  47                        "a" (0U), "d" (0U) : "ecx", "memory");
  48         ret = (((unsigned long long)edx) << 32) | ((unsigned long long)eax);
  49         if (ret)
  50                 return ret;
  51
  52         /*
  53          * Don't do an additional sync on CPUs where we know
  54          * RDTSC is already synchronous:
  55          */
  56         alternative_io("cpuid", ASM_NOP2, X86_FEATURE_SYNC_RDTSC,
  57                           "=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
  58
  59         return 0;
  60 }
  61
  62 static __always_inline cycles_t get_cycles_sync(void)
  63 {
  64         unsigned long long ret;
  65         ret = __get_cycles_sync();
  66         if (!ret)
  67                 rdtscll(ret);
  68         return ret;
  69 }
  70
  71 #ifdef CONFIG_PARAVIRT
  72 /*
  73  * For paravirt guests, some functionalities are executed through function
  74  * pointers in the various pvops structures.
  75  * These function pointers exist inside the kernel and can not
  76  * be accessed by user space. To avoid this, we make a copy of the
  77  * get_cycles_sync (called in kernel) but force the use of native_read_tsc.
  78  * Ideally, the guest should set up it's own clock and vread
  79  */
  80 static __always_inline long long vget_cycles_sync(void)
  81 {
  82         unsigned long long ret;
  83         ret = __get_cycles_sync();
  84         if (!ret)
  85                 ret = native_read_tsc();
  86         return ret;
  87 }
  88 #else
  89 # define vget_cycles_sync() get_cycles_sync()
  90 #endif
  91
  92 extern void tsc_init(void);
  93 extern void mark_tsc_unstable(char *reason);
  94 extern int unsynchronized_tsc(void);
  95 extern void init_tsc_clocksource(void);
  96 int check_tsc_unstable(void);
  97
  98 /*
  99  * Boot-time check whether the TSCs are synchronized across
 100  * all CPUs/cores:
 101  */
 102 extern void check_tsc_sync_source(int cpu);
 103 extern void check_tsc_sync_target(void);
 104
 105 extern void tsc_calibrate(void);
 106 extern int notsc_setup(char *);
 107
 108 #endif