runtime: use vDSO clock_gettime for time.now & runtime.nanotime on Linux/amd64

Performance improvement aside, time.Now() now gets real nanosecond resolution
on supported systems.

Benchmark done on Core i7-2600 @ 3.40GHz with kernel 3.5.2-gentoo.
original vDSO gettimeofday:
BenchmarkNow    100000000               27.4 ns/op
new vDSO gettimeofday fallback:
BenchmarkNow    100000000               27.6 ns/op
new vDSO clock_gettime:
BenchmarkNow    100000000               24.4 ns/op

R=golang-dev, bradfitz, iant, iant
CC=golang-dev
https://golang.org/cl/6814103

diff --git a/src/pkg/runtime/sys_linux_amd64.s b/src/pkg/runtime/sys_linux_amd64.s
index ca78ffa6f6e49c135267afe9440f0cbeef556f35..cb6f4a8ca0ed19f1f896bda3c56aad57efea2085 100644 (file)
--- a/src/pkg/runtime/sys_linux_amd64.s
+++ b/src/pkg/runtime/sys_linux_amd64.s
@@ -102,31 +102,37 @@ TEXT runtime·mincore(SB),7,$0-24
 
 // func now() (sec int64, nsec int32)
 TEXT time·now(SB), 7, $32
+       MOVQ    runtime·__vdso_clock_gettime_sym(SB), AX
+       CMPQ    AX, $0
+       JEQ     fallback_gtod
+       MOVL    $0, DI // CLOCK_REALTIME
+       LEAQ    8(SP), SI
+       CALL    AX
+       MOVQ    8(SP), AX       // sec
+       MOVQ    16(SP), DX      // nsec
+       MOVQ    AX, sec+0(FP)
+       MOVL    DX, nsec+8(FP)
+       RET
+fallback_gtod:
        LEAQ    8(SP), DI
        MOVQ    $0, SI
        MOVQ    runtime·__vdso_gettimeofday_sym(SB), AX
        CALL    AX
        MOVQ    8(SP), AX       // sec
        MOVL    16(SP), DX      // usec
-
-       // sec is in AX, usec in DX
-       MOVQ    AX, sec+0(FP)
        IMULQ   $1000, DX
+       MOVQ    AX, sec+0(FP)
        MOVL    DX, nsec+8(FP)
        RET
 
 TEXT runtime·nanotime(SB), 7, $32
-       LEAQ    8(SP), DI
-       MOVQ    $0, SI
-       MOVQ    $0xffffffffff600000, AX
-       CALL    AX
-       MOVQ    8(SP), AX       // sec
-       MOVL    16(SP), DX      // usec
+       CALL    time·now(SB)
+       MOVQ    0(SP), AX       // sec
+       MOVL    8(SP), DX       // nsec
 
        // sec is in AX, usec in DX
        // return nsec in AX
        IMULQ   $1000000000, AX
-       IMULQ   $1000, DX
        ADDQ    DX, AX
        RET
 

diff --git a/src/pkg/runtime/vdso_linux_amd64.c b/src/pkg/runtime/vdso_linux_amd64.c
index 923bab0c2b9db91f5dd7897fb53fdec0abc4a49d..b125c8b05109486b8c26e0d4f409435fd96dc00f 100644 (file)
--- a/src/pkg/runtime/vdso_linux_amd64.c
+++ b/src/pkg/runtime/vdso_linux_amd64.c
@@ -161,11 +161,13 @@ static version_key linux26 = { (byte*)"LINUX_2.6", 0x3ae75f6 };
 // initialize with vsyscall fallbacks
 void* runtime·__vdso_time_sym = (void*)0xffffffffff600400ULL;
 void* runtime·__vdso_gettimeofday_sym = (void*)0xffffffffff600000ULL;
+void* runtime·__vdso_clock_gettime_sym = (void*)0;
 
-#define SYM_KEYS_COUNT 2
+#define SYM_KEYS_COUNT 3
 static symbol_key sym_keys[] = {
        { (byte*)"__vdso_time", &runtime·__vdso_time_sym },
        { (byte*)"__vdso_gettimeofday", &runtime·__vdso_gettimeofday_sym },
+       { (byte*)"__vdso_clock_gettime", &runtime·__vdso_clock_gettime_sym },
 };
 
 static void vdso_init_from_sysinfo_ehdr(struct vdso_info *vdso_info, Elf64_Ehdr* hdr) {