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May 24, 2018 03:03
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| package main | |
| import ( | |
| "testing" | |
| "time" | |
| ) | |
| func BenchmarkTimeNow(b *testing.B) { | |
| for i := 0; i < b.N; i++ { | |
| time.Now() | |
| } | |
| } | |
| // goos: linux | |
| // goarch: amd64 | |
| // BenchmarkTimeNow-2 500000 3758 ns/op |
> go version
go version devel +65c365bf0f Wed May 23 23:51:30 2018 +0000 linux/amd64
> go test -bench . -cpuprofile cpu.out
goos: linux
goarch: amd64
BenchmarkTimeNow-2 500000 3753 ns/op
PASS
ok _/tmp/test 2.109s
> go tool pprof test.test cpu.out
File: test.test
Type: cpu
Time: May 24, 2018 at 9:36pm (CST)
Duration: 2.10s, Total samples = 1.91s (90.78%!)(MISSING)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) top
Showing nodes accounting for 1910ms, 100% of 1910ms total
flat flat% sum% cum cum%
1890ms 98.95% 98.95% 1890ms 98.95% time.now
20ms 1.05% 100% 60ms 3.14% time.Now
0 0% 100% 60ms 3.14% _/tmp/test.BenchmarkTimeNow
0 0% 100% 60ms 3.14% testing.(*B).autodetectN
0 0% 100% 60ms 3.14% testing.(*B).launch
0 0% 100% 60ms 3.14% testing.(*B).runN
(pprof) list time.Now
Total: 1.91s
ROUTINE ======================== time.Now in /home/rany/Development/Tools/go/src/time/time.go
20ms 60ms (flat, cum) 3.14% of Total
. . 1050:// Provided by package runtime.
. . 1051:func now() (sec int64, nsec int32, mono int64)
. . 1052:
. . 1053:// Now returns the current local time.
. . 1054:func Now() Time {
20ms 60ms 1055: sec, nsec, mono := now()
. . 1056: sec += unixToInternal - minWall
. . 1057: if uint64(sec)>>33 != 0 {
. . 1058: return Time{uint64(nsec), sec + minWall, Local}
. . 1059: }
. . 1060: return Time{hasMonotonic | uint64(sec)<<nsecShift | uint64(nsec), mono, Local}
(pprof) list time.now
Total: 1.91s
ROUTINE ======================== time.now in /home/rany/Development/Tools/go/src/runtime/timestub.go
1.89s 1.89s (flat, cum) 98.95% of Total
. . 12:
. . 13:import _ "unsafe" // for go:linkname
. . 14:
. . 15://go:linkname time_now time.now
. . 16:func time_now() (sec int64, nsec int32, mono int64) {
980ms 980ms 17: sec, nsec = walltime()
910ms 910ms 18: return sec, nsec, nanotime() - startNano
. . 19:}
(pprof) exit
> export GOROOT=/tmp/go1.8
> export PATH=/tmp/go1.8/bin
> go version
go version go1.8 linux/amd64
> go test -bench . -cpuprofile cpu.out
BenchmarkTimeNow-2 1000000 1825 ns/op
PASS
ok _/tmp/test 1.853s
> go tool pprof test.test cpu.out
Entering interactive mode (type "help" for commands)
(pprof) top
1.83s of 1.83s total ( 100%)
flat flat% sum% cum cum%
1.78s 97.27% 97.27% 1.78s 97.27% runtime._ExternalCode
0.04s 2.19% 99.45% 0.05s 2.73% time.Now
0.01s 0.55% 100% 0.01s 0.55% time.now
0 0% 100% 0.05s 2.73% _/tmp/test.BenchmarkTimeNow
0 0% 100% 1.78s 97.27% runtime._System
0 0% 100% 0.05s 2.73% runtime.goexit
0 0% 100% 0.05s 2.73% testing.(*B).launch
0 0% 100% 0.05s 2.73% testing.(*B).runN
(pprof) list time.Now
Total: 1.83s
ROUTINE ======================== time.Now in /tmp/go1.8/src/time/time.go
40ms 50ms (flat, cum) 2.73% of Total
. . 792:
. . 793:// Provided by package runtime.
. . 794:func now() (sec int64, nsec int32)
. . 795:
. . 796:// Now returns the current local time.
10ms 10ms 797:func Now() Time {
20ms 30ms 798: sec, nsec := now()
10ms 10ms 799: return Time{sec + unixToInternal, nsec, Local}
. . 800:}
. . 801:
. . 802:// UTC returns t with the location set to UTC.
. . 803:func (t Time) UTC() Time {
. . 804: t.setLoc(&utcLoc)
(pprof) list time.now
Total: 1.83s
ROUTINE ======================== time.now in /tmp/go1.8/src/runtime/sys_linux_amd64.s
10ms 10ms (flat, cum) 0.55% of Total
. . 146: JEQ fallback
. . 147: MOVL $0, DI // CLOCK_REALTIME
. . 148: LEAQ 0(SP), SI
. . 149: CALL AX
. . 150: MOVQ 0(SP), AX // sec
10ms 10ms 151: MOVQ 8(SP), DX // nsec
. . 152: MOVQ AX, sec+0(FP)
. . 153: MOVL DX, nsec+8(FP)
. . 154: RET
. . 155:fallback:
. . 156: LEAQ 0(SP), DI
(pprof)
Also tested on Go 1.10.2 tarball downloaded directly from Golang website. It still slow but the profile information is differ.
> export GOROOT=/tmp/go1.10.2
> export PATH=/tmp/go1.10.2/bin
> go version
go version go1.10.2 linux/amd64
> go test -bench . -cpuprofile cpu.out
goos: linux
goarch: amd64
BenchmarkTimeNow-2 500000 3632 ns/op
PASS
ok _/tmp/test 2.009s
> go tool pprof test.test cpu.out
File: test.test
Type: cpu
Time: May 24, 2018 at 10:44pm (CST)
Duration: 2s, Total samples = 1.86s (92.86%)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) top
Showing nodes accounting for 1.86s, 100% of 1.86s total
flat flat% sum% cum cum%
1.76s 94.62% 94.62% 1.76s 94.62% runtime._ExternalCode
0.04s 2.15% 96.77% 0.04s 2.15% runtime.nanotime
0.04s 2.15% 98.92% 0.07s 3.76% time.now
0.01s 0.54% 99.46% 0.08s 4.30% _/tmp/test.BenchmarkTimeNow
0.01s 0.54% 100% 0.01s 0.54% runtime.walltime
0 0% 100% 1.78s 95.70% runtime._System
0 0% 100% 0.08s 4.30% testing.(*B).launch
0 0% 100% 0.08s 4.30% testing.(*B).runN
0 0% 100% 0.07s 3.76% time.Now
(pprof) list time.Now
Total: 1.86s
ROUTINE ======================== time.Now in /tmp/go1.10.2/src/time/time.go
0 70ms (flat, cum) 3.76% of Total
. . 1039:// Provided by package runtime.
. . 1040:func now() (sec int64, nsec int32, mono int64)
. . 1041:
. . 1042:// Now returns the current local time.
. . 1043:func Now() Time {
. 70ms 1044: sec, nsec, mono := now()
. . 1045: sec += unixToInternal - minWall
. . 1046: if uint64(sec)>>33 != 0 {
. . 1047: return Time{uint64(nsec), sec + minWall, Local}
. . 1048: }
. . 1049: return Time{hasMonotonic | uint64(sec)<<nsecShift | uint64(nsec), mono, Local}
(pprof) list time.now
Total: 1.86s
ROUTINE ======================== time.now in /tmp/go1.10.2/src/runtime/timestub.go
40ms 70ms (flat, cum) 3.76% of Total
. . 14:
. . 15:func walltime() (sec int64, nsec int32)
. . 16:
. . 17://go:linkname time_now time.now
. . 18:func time_now() (sec int64, nsec int32, mono int64) {
20ms 20ms 19: sec, nsec = walltime()
20ms 50ms 20: return sec, nsec, nanotime() - startNano
. . 21:}
(pprof)
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Discussion on the performance problem: https://groups.google.com/forum/#!topic/golang-nuts/7HybUAvUge4
Much more detail: