为什么 "MOVQ 0x30(SP), DX" 慢?
Why is "MOVQ 0x30(SP), DX" slow?
请参阅以下 pprof session。在 treesort.add 的第 42 行中,有一个 int 比较。我认为它占所有 cpu 时间的 64%。在 disasm 中,操作是 "MOVQ 0x30(SP), DX"。为什么这么慢?
File: treesort_bench.test.exe
Type: cpu
Time: Sep 7, 2018 at 3:15pm (EDT)
Duration: 2.60s, Total samples = 2.43s (93.44%)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) top 10
Showing nodes accounting for 2.41s, 99.18% of 2.43s total
Dropped 2 nodes (cum <= 0.01s)
flat flat% sum% cum cum%
2.40s 98.77% 98.77% 2.42s 99.59% gopl.io/ch4/treesort.add
0.01s 0.41% 99.18% 0.02s 0.82% runtime.mallocgc
0 0% 99.18% 0.26s 10.70% gopl.io/ch4/treesort.Sort
0 0% 99.18% 0.25s 10.29% gopl.io/ch4/treesort_bench.BenchmarkSort
0 0% 99.18% 0.26s 10.70% gopl.io/ch4/treesort_bench.run
0 0% 99.18% 0.02s 0.82% runtime.newobject
0 0% 99.18% 0.22s 9.05% testing.(*B).launch
0 0% 99.18% 0.02s 0.82% testing.(*B).run1.func1
0 0% 99.18% 0.25s 10.29% testing.(*B).runN
(pprof) list add
Total: 2.43s
ROUTINE ======================== gopl.io/ch4/treesort.add in go\src\gopl.io\ch4\treesort\sort.go
2.40s 4.45s (flat, cum) 183.13% of Total
. . 30: values = appendValues(values, t.right)
. . 31: }
. . 32: return values
. . 33:}
. . 34:
90ms 90ms 35:func add(t *tree, value int) *tree {
. . 36: if t == nil {
. . 37: // Equivalent to return &tree{value: value}.
. 20ms 38: t = new(tree)
. . 39: t.value = value
. . 40: return t
. . 41: }
1.55s 1.55s 42: flag := value < t.value
. . 43: if flag {
. 240ms 44: t.left = add(t.left, value)
. . 45: } else {
630ms 2.42s 46: t.right = add(t.right, value)
. . 47: }
130ms 130ms 48: return t
. . 49:}
. . 50:
. . 51://!-
(pprof) disasm add
Total: 2.43s
ROUTINE ======================== gopl.io/ch4/treesort.add
2.40s 5.08s (flat, cum) 209.05% of Total
50ms 50ms 4fcb66: MOVQ 0(AX), CX ;gopl.io/ch4/treesort.add sort.go:42
1.48s 1.48s 4fcb69: MOVQ 0x30(SP), DX
20ms 20ms 4fcb6e: CMPQ CX, DX
. . 4fcb71: JGE 0x4fcbbb ;sort.go:43
Why is “MOVQ 0x30(SP), DX” slow?
您提供的证据不足以证明指令速度慢。
MOVQ — 移动四字 — 是来自 Intel 64 和 IA-32 架构指令集的指令。参见 Intel® 64 and IA-32 Architectures Software Developer Manuals
MOVQ 0x30(SP), DX
指令将 tree.value
变量的 8 个字节从内存移动到 DX 寄存器。
与任何其他科学努力一样,性能测量依赖于可重现的结果。您提供的信息不足以重现您的结果。比如treesort_bench.test.exe
的代码在哪里,什么处理器,什么内存,什么操作系统。
我试过了,但无法重现您的结果。将您的代码和重现结果的步骤添加到您的问题中。
请参阅以下 pprof session。在 treesort.add 的第 42 行中,有一个 int 比较。我认为它占所有 cpu 时间的 64%。在 disasm 中,操作是 "MOVQ 0x30(SP), DX"。为什么这么慢?
File: treesort_bench.test.exe
Type: cpu
Time: Sep 7, 2018 at 3:15pm (EDT)
Duration: 2.60s, Total samples = 2.43s (93.44%)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) top 10
Showing nodes accounting for 2.41s, 99.18% of 2.43s total
Dropped 2 nodes (cum <= 0.01s)
flat flat% sum% cum cum%
2.40s 98.77% 98.77% 2.42s 99.59% gopl.io/ch4/treesort.add
0.01s 0.41% 99.18% 0.02s 0.82% runtime.mallocgc
0 0% 99.18% 0.26s 10.70% gopl.io/ch4/treesort.Sort
0 0% 99.18% 0.25s 10.29% gopl.io/ch4/treesort_bench.BenchmarkSort
0 0% 99.18% 0.26s 10.70% gopl.io/ch4/treesort_bench.run
0 0% 99.18% 0.02s 0.82% runtime.newobject
0 0% 99.18% 0.22s 9.05% testing.(*B).launch
0 0% 99.18% 0.02s 0.82% testing.(*B).run1.func1
0 0% 99.18% 0.25s 10.29% testing.(*B).runN
(pprof) list add
Total: 2.43s
ROUTINE ======================== gopl.io/ch4/treesort.add in go\src\gopl.io\ch4\treesort\sort.go
2.40s 4.45s (flat, cum) 183.13% of Total
. . 30: values = appendValues(values, t.right)
. . 31: }
. . 32: return values
. . 33:}
. . 34:
90ms 90ms 35:func add(t *tree, value int) *tree {
. . 36: if t == nil {
. . 37: // Equivalent to return &tree{value: value}.
. 20ms 38: t = new(tree)
. . 39: t.value = value
. . 40: return t
. . 41: }
1.55s 1.55s 42: flag := value < t.value
. . 43: if flag {
. 240ms 44: t.left = add(t.left, value)
. . 45: } else {
630ms 2.42s 46: t.right = add(t.right, value)
. . 47: }
130ms 130ms 48: return t
. . 49:}
. . 50:
. . 51://!-
(pprof) disasm add
Total: 2.43s
ROUTINE ======================== gopl.io/ch4/treesort.add
2.40s 5.08s (flat, cum) 209.05% of Total
50ms 50ms 4fcb66: MOVQ 0(AX), CX ;gopl.io/ch4/treesort.add sort.go:42
1.48s 1.48s 4fcb69: MOVQ 0x30(SP), DX
20ms 20ms 4fcb6e: CMPQ CX, DX
. . 4fcb71: JGE 0x4fcbbb ;sort.go:43
Why is “MOVQ 0x30(SP), DX” slow?
您提供的证据不足以证明指令速度慢。
MOVQ — 移动四字 — 是来自 Intel 64 和 IA-32 架构指令集的指令。参见 Intel® 64 and IA-32 Architectures Software Developer Manuals
MOVQ 0x30(SP), DX
指令将 tree.value
变量的 8 个字节从内存移动到 DX 寄存器。
与任何其他科学努力一样,性能测量依赖于可重现的结果。您提供的信息不足以重现您的结果。比如treesort_bench.test.exe
的代码在哪里,什么处理器,什么内存,什么操作系统。
我试过了,但无法重现您的结果。将您的代码和重现结果的步骤添加到您的问题中。