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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
This commit is contained in:
Shenghou Ma 2012-11-09 14:19:07 +08:00
parent f668e0a5b3
commit 4022fc4e21
2 changed files with 19 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
src/pkg/runtime/sys_linux_amd64.s
View File

@ -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

4
src/pkg/runtime/vdso_linux_amd64.c
View File

@ -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) {