xnu-7195.101.1.tar.gz

[apple/xnu.git] / osfmk / i386 / rtclock_asm_native.h

diff --git a/osfmk/i386/rtclock_asm_native.h b/osfmk/i386/rtclock_asm_native.h
index c17320b7a667c89861396cc947ce5933786e1436..50919f1fd8819093f8a009651f9a5d9b79b0a802 100644 (file)
--- a/osfmk/i386/rtclock_asm_native.h
+++ b/osfmk/i386/rtclock_asm_native.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010 Apple Inc. All rights reserved.
+ * Copyright (c) 2010-2012 Apple Inc. All rights reserved.
  *
  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
  * 
@@ -39,39 +39,27 @@
 #ifndef _PAL_RTCLOCK_ASM_NATIVE_H_
 #define _PAL_RTCLOCK_ASM_NATIVE_H_
 
-
-#if defined(__i386__)
-/*
- * Assembly snippet included in exception handlers and rtc_nanotime_read()
- * %edi points to nanotime info struct
- * %edx:%eax returns nanotime
- */
-#define PAL_RTC_NANOTIME_READ_FAST()                                     \
-0:     movl    RNT_GENERATION(%edi),%esi       /* being updated? */    ; \
-       testl   %esi,%esi                                               ; \
-       jz      0b                              /* wait until done */   ; \
-       lfence                                                          ; \
-       rdtsc                                                           ; \
-       lfence                                                          ; \
-       subl    RNT_TSC_BASE(%edi),%eax                                 ; \
-       sbbl    RNT_TSC_BASE+4(%edi),%edx       /* tsc - tsc_base */    ; \
-       movl    RNT_SCALE(%edi),%ecx            /* * scale factor */    ; \
-       movl    %edx,%ebx                                               ; \
-       mull    %ecx                                                    ; \
-       movl    %ebx,%eax                                               ; \
-       movl    %edx,%ebx                                               ; \
-       mull    %ecx                                                    ; \
-       addl    %ebx,%eax                                               ; \
-       adcl    $0,%edx                                                 ; \
-       addl    RNT_NS_BASE(%edi),%eax          /* + ns_base */         ; \
-       adcl    RNT_NS_BASE+4(%edi),%edx                                ; \
-       cmpl    RNT_GENERATION(%edi),%esi       /* check for update */  ; \
-       jne     0b                              /* do it all again */
-
-#elif defined(__x86_64__)
-
 /*
  * Assembly snippet included in exception handlers and rtc_nanotime_read()
+ *
+ *
+ * Warning!  There are several copies of this code in the trampolines found in
+ * osfmk/x86_64/idt64.s, coming from the various TIMER macros in rtclock_asm.h.
+ * They're all kept in sync by using the RTC_NANOTIME_READ() macro.
+ *
+ * The algorithm we use is:
+ *
+ *     ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)*rnt_tsc_scale) / 2**32) + rnt_ns_base;
+ *
+ * rnt_shift, a constant computed during initialization, is the smallest value for which:
+ *
+ *     (tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD
+ *
+ * Where SLOW_TSC_THRESHOLD is about 10e9.  Since most processor's tscFreqs are greater
+ * than 1GHz, rnt_shift is usually 0.  rnt_tsc_scale is also a 32-bit constant:
+ *
+ *     rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift);
+ *
  * %rdi points to nanotime info struct.
  * %rax returns nanotime
  */
@@ -81,11 +69,11 @@
         jz        0b                   /* - wait if so */              ; \
        lfence                                                          ; \
        rdtsc                                                           ; \
-       lfence                                                          ; \
        shlq    $32,%rdx                                                ; \
+       movl    RNT_SHIFT(%rdi),%ecx                                    ; \
        orq     %rdx,%rax                       /* %rax := tsc */       ; \
        subq    RNT_TSC_BASE(%rdi),%rax         /* tsc - tsc_base */    ; \
-       xorq    %rcx,%rcx                                               ; \
+       shlq    %cl,%rax                                                ; \
        movl    RNT_SCALE(%rdi),%ecx                                    ; \
        mulq    %rcx                            /* delta * scale */     ; \
        shrdq   $32,%rdx,%rax                   /* %rdx:%rax >>= 32 */  ; \
@@ -93,7 +81,21 @@
        cmpl    RNT_GENERATION(%rdi),%esi       /* repeat if changed */ ; \
        jne     0b
 
-#endif /* !defined(x86_64) */
-
+#define PAL_RTC_NANOTIME_READ_NOBARRIER()                                        \
+0:     movl    RNT_GENERATION(%rdi),%esi                               ; \
+       test        %esi,%esi           /* info updating? */            ; \
+        jz        0b                   /* - wait if so */              ; \
+       rdtsc                                                           ; \
+       shlq    $32,%rdx                                                ; \
+       movl    RNT_SHIFT(%rdi),%ecx                                    ; \
+       orq     %rdx,%rax                       /* %rax := tsc */       ; \
+       subq    RNT_TSC_BASE(%rdi),%rax         /* tsc - tsc_base */    ; \
+       shlq    %cl,%rax                                                ; \
+       movl    RNT_SCALE(%rdi),%ecx                                    ; \
+       mulq    %rcx                            /* delta * scale */     ; \
+       shrdq   $32,%rdx,%rax                   /* %rdx:%rax >>= 32 */  ; \
+       addq    RNT_NS_BASE(%rdi),%rax          /* add ns_base */       ; \
+       cmpl    RNT_GENERATION(%rdi),%esi       /* repeat if changed */ ; \
+       jne     0b
 
 #endif /* _PAL_RTCLOCK_ASM_NATIVE_H_ */