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34 /*

35 * File: rtclock_asm_native.h

36 * Purpose: Native routines for reading nanotime

37 */

38

39 #ifndef _PAL_RTCLOCK_ASM_NATIVE_H_

40 #define _PAL_RTCLOCK_ASM_NATIVE_H_

41

42 /*

43 * Assembly snippet included in exception handlers and rtc_nanotime_read()

44 *

45 *

46 * Warning! There are several copies of this code in the trampolines found in

47 * osfmk/x86_64/idt64.s, coming from the various TIMER macros in rtclock_asm.h.

48 * They're all kept in sync by using the RTC_NANOTIME_READ() macro.

49 *

50 * The algorithm we use is:

51 *

52 * ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)*rnt_tsc_scale) / 2**32) + rnt_ns_base;

53 *

54 * rnt_shift, a constant computed during initialization, is the smallest value for which:

55 *

56 * (tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD

57 *

58 * Where SLOW_TSC_THRESHOLD is about 10e9. Since most processor's tscFreqs are greater

59 * than 1GHz, rnt_shift is usually 0. rnt_tsc_scale is also a 32-bit constant:

60 *

61 * rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift);

62 *

63 * %rdi points to nanotime info struct.

64 * %rax returns nanotime

65 */

66 #define PAL_RTC_NANOTIME_READ_FAST() \

67 0: movl RNT_GENERATION(%rdi),%esi ; \

68 test %esi,%esi /* info updating? */ ; \

69 jz 0b /* - wait if so */ ; \

70 lfence ; \

71 rdtsc ; \

72 shlq $32,%rdx ; \

73 movl RNT_SHIFT(%rdi),%ecx ; \

74 orq %rdx,%rax /* %rax := tsc */ ; \

75 subq RNT_TSC_BASE(%rdi),%rax /* tsc - tsc_base */ ; \

76 shlq %cl,%rax ; \

77 movl RNT_SCALE(%rdi),%ecx ; \

78 mulq %rcx /* delta * scale */ ; \

79 shrdq $32,%rdx,%rax /* %rdx:%rax >>= 32 */ ; \

80 addq RNT_NS_BASE(%rdi),%rax /* add ns_base */ ; \

81 cmpl RNT_GENERATION(%rdi),%esi /* repeat if changed */ ; \

82 jne 0b

83

84 #define PAL_RTC_NANOTIME_READ_NOBARRIER() \

85 0: movl RNT_GENERATION(%rdi),%esi ; \

86 test %esi,%esi /* info updating? */ ; \

87 jz 0b /* - wait if so */ ; \

88 rdtsc ; \

89 shlq $32,%rdx ; \

90 movl RNT_SHIFT(%rdi),%ecx ; \

91 orq %rdx,%rax /* %rax := tsc */ ; \

92 subq RNT_TSC_BASE(%rdi),%rax /* tsc - tsc_base */ ; \

93 shlq %cl,%rax ; \

94 movl RNT_SCALE(%rdi),%ecx ; \

95 mulq %rcx /* delta * scale */ ; \

96 shrdq $32,%rdx,%rax /* %rdx:%rax >>= 32 */ ; \

97 addq RNT_NS_BASE(%rdi),%rax /* add ns_base */ ; \

98 cmpl RNT_GENERATION(%rdi),%esi /* repeat if changed */ ; \

99 jne 0b

100

101 #endif /* _PAL_RTCLOCK_ASM_NATIVE_H_ */