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avinoamr opened this issue Apr 25, 2017 · 1 comment
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Interface function invocation is horribly slow? #20116

avinoamr opened this issue Apr 25, 2017 · 1 comment
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@avinoamr
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avinoamr commented Apr 25, 2017 •
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I've had several types implementing the same interface. Invoking functions on the interface had horrible performance compared to running them on the concrete type:

import "testing"

type D interface {
    Append(D)
}

type Strings []string

func (s Strings) Append(d D) {}

func BenchmarkInterface(b *testing.B) {
    s := D(Strings{})
    for i := 0 ; i < b.N ; i += 1 {
        s.Append(Strings{""})
    }
}

func BenchmarkConcrete(b *testing.B) {
    s := Strings{} // only difference is that I'm not casting it to the generic interface
    for i := 0 ; i < b.N ; i += 1 {
        s.Append(Strings{""})
    }
}

These are the results I'm seeing:

BenchmarkInterface-4     	20000000	        74.6 ns/op
BenchmarkConcrete-4   	2000000000	         1.67 ns/op

Does it make any sense that using the concrete type is 45x faster? The only solution I could find is to use a type-switch everywhere I run this function.

When I remove the argument from the function definition (or replace it with an int), the runtime drops significantly. There's still a big difference but one that makes more sense to me. I suspect that it might be related to mem-copies?

$ go version
go version go1.8.1 darwin/amd64

$ go env
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/avinoamr/go"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.8.1/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.8.1/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/01/m48g6qr573b8_dvmdfr_nw1h0000gn/T/go-build557172691=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
@bradfitz
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This is due to inlining and escape analysis, not the call overhead itself. The compiler can prove to itself more about code with concrete types.

Compare:

$ go tool compile -m concrete_test.go
concrete_test.go:11:6: can inline Strings.Append
concrete_test.go:18:11: inlining call to Strings.Append
concrete_test.go:11:27: Strings.Append s does not escape
concrete_test.go:11:27: Strings.Append d does not escape
concrete_test.go:15:27: BenchmarkConcrete b does not escape
concrete_test.go:16:14: BenchmarkConcrete Strings literal does not escape
concrete_test.go:18:19: BenchmarkConcrete Strings literal does not escape
concrete_test.go:18:19: BenchmarkConcrete Strings literal does not escape
<autogenerated>:1:0: leaking param: .anon0
<autogenerated>:1:0: leaking param: .this
<autogenerated>:1:0: inlining call to Strings.Append
<autogenerated>:1:0: (*Strings).Append .this does not escape
<autogenerated>:1:0: (*Strings).Append d does not escape
<autogenerated>:1:0: leaking param: .this
<autogenerated>:1:0: leaking param: .this

"".BenchmarkConcrete STEXT nosplit size=98 args=0x8 locals=0x30
        0x0000 00000 (concrete_test.go:15)      TEXT    "".BenchmarkConcrete(SB), NOSPLIT, $48-8
        0x0000 00000 (concrete_test.go:15)      SUBQ    $48, SP
        0x0004 00004 (concrete_test.go:15)      MOVQ    BP, 40(SP)
        0x0009 00009 (concrete_test.go:15)      LEAQ    40(SP), BP
        0x000e 00014 (concrete_test.go:15)      FUNCDATA        $0, gclocals·a36216b97439c93dafebe03e7f0808b5(SB)                                     
        0x000e 00014 (concrete_test.go:15)      FUNCDATA        $1, gclocals·24b0aee1021c20d1590e75b99691b0e0(SB)
        0x000e 00014 (concrete_test.go:17)      MOVQ    "".b+56(SP), AX
        0x0013 00019 (concrete_test.go:16)      MOVQ    $0, CX
        0x0015 00021 (concrete_test.go:17)      JMP     76
        0x0017 00023 (concrete_test.go:18)      MOVQ    "".statictmp_0(SB), DX
        0x001e 00030 (concrete_test.go:18)      MOVQ    "".statictmp_0+8(SB), BX
        0x0025 00037 (concrete_test.go:18)      MOVQ    DX, ""..autotmp_12(SP)
        0x0029 00041 (concrete_test.go:18)      MOVQ    BX, ""..autotmp_12+8(SP)
        0x002e 00046 (concrete_test.go:18)      LEAQ    ""..autotmp_12(SP), DX
        0x0032 00050 (concrete_test.go:18)      MOVQ    DX, ""..autotmp_15+16(SP)                                                                     
        0x0037 00055 (concrete_test.go:18)      MOVQ    $1, ""..autotmp_15+24(SP)
        0x0040 00064 (concrete_test.go:18)      MOVQ    $1, ""..autotmp_15+32(SP)
        0x0049 00073 (concrete_test.go:17)      INCQ    CX
        0x004c 00076 (concrete_test.go:17)      MOVQ    240(AX), DX
        0x0053 00083 (concrete_test.go:17)      CMPQ    CX, DX
        0x0056 00086 (concrete_test.go:17)      JLT     23
        0x0058 00088 (concrete_test.go:20)      MOVQ    40(SP), BP
        0x005d 00093 (concrete_test.go:20)      ADDQ    $48, SP
        0x0061 00097 (concrete_test.go:20)      RET

vs.

$ go tool compile -m interface_test.go
interface_test.go:11:6: can inline Strings.Append
interface_test.go:11:27: Strings.Append s does not escape
interface_test.go:11:27: Strings.Append d does not escape
interface_test.go:18:19: Strings literal escapes to heap
interface_test.go:18:19: Strings literal escapes to heap
interface_test.go:16:8: D(Strings literal) escapes to heap
interface_test.go:16:16: Strings literal escapes to heap
interface_test.go:15:28: BenchmarkInterface b does not escape
<autogenerated>:1:0: leaking param: .anon0
<autogenerated>:1:0: leaking param: .this
<autogenerated>:1:0: inlining call to Strings.Append
<autogenerated>:1:0: (*Strings).Append .this does not escape
<autogenerated>:1:0: (*Strings).Append d does not escape
<autogenerated>:1:0: leaking param: .this
<autogenerated>:1:0: leaking param: .this

"".BenchmarkInterface STEXT size=392 args=0x8 locals=0x80
        0x0000 00000 (interface_test.go:15)     TEXT    "".BenchmarkInterface(SB), $128-8                                                             
        0x0000 00000 (interface_test.go:15)     MOVQ    (TLS), CX
        0x0009 00009 (interface_test.go:15)     CMPQ    SP, 16(CX)
        0x000d 00013 (interface_test.go:15)     JLS     382
        0x0013 00019 (interface_test.go:15)     SUBQ    $128, SP
        0x001a 00026 (interface_test.go:15)     MOVQ    BP, 120(SP)
        0x001f 00031 (interface_test.go:15)     LEAQ    120(SP), BP
        0x0024 00036 (interface_test.go:15)     FUNCDATA        $0, gclocals·7c2b9c64f1281cf71d4e337ac2ec0e62(SB)
        0x0024 00036 (interface_test.go:15)     FUNCDATA        $1, gclocals·1c3074cffd902186c29a0dd59f96868f(SB)
        0x0024 00036 (interface_test.go:16)     LEAQ    type.[0]string(SB), AX
        0x002b 00043 (interface_test.go:16)     MOVQ    AX, (SP)
        0x002f 00047 (interface_test.go:16)     PCDATA  $0, $0
        0x002f 00047 (interface_test.go:16)     CALL    runtime.newobject(SB)
        0x0034 00052 (interface_test.go:16)     MOVQ    8(SP), AX
        0x0039 00057 (interface_test.go:16)     MOVQ    AX, ""..autotmp_3+96(SP)
        0x003e 00062 (interface_test.go:16)     MOVQ    $0, ""..autotmp_3+104(SP)
        0x0047 00071 (interface_test.go:16)     MOVQ    $0, ""..autotmp_3+112(SP)
        0x0050 00080 (interface_test.go:16)     LEAQ    go.itab."".Strings,"".D(SB), AX
        0x0057 00087 (interface_test.go:16)     MOVQ    AX, (SP)
        0x005b 00091 (interface_test.go:16)     LEAQ    ""..autotmp_3+96(SP), CX
        0x0060 00096 (interface_test.go:16)     MOVQ    CX, 8(SP)
        0x0065 00101 (interface_test.go:16)     PCDATA  $0, $1
        0x0065 00101 (interface_test.go:16)     CALL    runtime.convT2Islice(SB)                                                                      
        0x006a 00106 (interface_test.go:16)     MOVQ    16(SP), AX
        0x006f 00111 (interface_test.go:16)     MOVQ    AX, "".s.itab+48(SP)                                                                          
        0x0074 00116 (interface_test.go:16)     MOVQ    24(SP), CX
        0x0079 00121 (interface_test.go:16)     MOVQ    CX, "".s.data+56(SP)
        0x007e 00126 (interface_test.go:16)     MOVQ    $0, DX
        0x0080 00128 (interface_test.go:17)     JMP     314
        0x0085 00133 (interface_test.go:17)     MOVQ    DX, "".i+32(SP)
        0x008a 00138 (interface_test.go:18)     LEAQ    type.[1]string(SB), AX
        0x0091 00145 (interface_test.go:18)     MOVQ    AX, (SP)
        0x0095 00149 (interface_test.go:18)     PCDATA  $0, $2
        0x0095 00149 (interface_test.go:18)     CALL    runtime.newobject(SB)
        0x009a 00154 (interface_test.go:18)     MOVQ    "".statictmp_0+8(SB), AX
        0x00a1 00161 (interface_test.go:18)     MOVQ    8(SP), CX
        0x00a6 00166 (interface_test.go:18)     MOVQ    "".statictmp_0(SB), DX
        0x00ad 00173 (interface_test.go:18)     MOVQ    AX, 8(CX)
        0x00b1 00177 (interface_test.go:18)     MOVL    runtime.writeBarrier(SB), AX
        0x00b7 00183 (interface_test.go:18)     TESTL   AX, AX
        0x00b9 00185 (interface_test.go:18)     JNE     340
        0x00bf 00191 (interface_test.go:18)     MOVQ    DX, (CX)
        0x00c2 00194 (interface_test.go:18)     TESTB   AL, (CX)
        0x00c4 00196 (interface_test.go:18)     MOVQ    CX, ""..autotmp_4+72(SP)
        0x00c9 00201 (interface_test.go:18)     MOVQ    $1, ""..autotmp_4+80(SP)
        0x00d2 00210 (interface_test.go:18)     MOVQ    $1, ""..autotmp_4+88(SP)
        0x00db 00219 (interface_test.go:18)     MOVQ    "".s.itab+48(SP), AX
        0x00e0 00224 (interface_test.go:18)     MOVQ    32(AX), CX
        0x00e4 00228 (interface_test.go:18)     MOVQ    CX, ""..autotmp_12+40(SP)
        0x00e9 00233 (interface_test.go:16)     LEAQ    go.itab."".Strings,"".D(SB), DX
        0x00f0 00240 (interface_test.go:18)     MOVQ    DX, (SP)
        0x00f4 00244 (interface_test.go:18)     LEAQ    ""..autotmp_4+72(SP), BX                                                                      
        0x00f9 00249 (interface_test.go:18)     MOVQ    BX, 8(SP)
        0x00fe 00254 (interface_test.go:18)     PCDATA  $0, $3
        0x00fe 00254 (interface_test.go:18)     CALL    runtime.convT2Islice(SB)
        0x0103 00259 (interface_test.go:18)     MOVQ    16(SP), AX
        0x0108 00264 (interface_test.go:18)     MOVQ    24(SP), CX
        0x010d 00269 (interface_test.go:18)     MOVQ    AX, 8(SP)
        0x0112 00274 (interface_test.go:18)     MOVQ    CX, 16(SP)
        0x0117 00279 (interface_test.go:18)     MOVQ    "".s.data+56(SP), AX
        0x011c 00284 (interface_test.go:18)     MOVQ    AX, (SP)
        0x0120 00288 (interface_test.go:18)     MOVQ    ""..autotmp_12+40(SP), CX
        0x0125 00293 (interface_test.go:18)     PCDATA  $0, $3
        0x0125 00293 (interface_test.go:18)     CALL    CX
        0x0127 00295 (interface_test.go:17)     MOVQ    "".i+32(SP), AX
        0x012c 00300 (interface_test.go:17)     LEAQ    1(AX), DX
        0x0130 00304 (interface_test.go:18)     MOVQ    "".s.itab+48(SP), AX
        0x0135 00309 (interface_test.go:18)     MOVQ    "".s.data+56(SP), CX
        0x013a 00314 (interface_test.go:17)     MOVQ    "".b+136(SP), BX
        0x0142 00322 (interface_test.go:17)     MOVQ    240(BX), SI
        0x0149 00329 (interface_test.go:17)     CMPQ    DX, SI
        0x014c 00332 (interface_test.go:17)     JLT     133
        0x0152 00338 (interface_test.go:17)     JMP     369
        0x0154 00340 (interface_test.go:18)     MOVQ    CX, ""..autotmp_13+64(SP)
        0x0159 00345 (interface_test.go:18)     MOVQ    CX, (SP)
        0x015d 00349 (interface_test.go:18)     MOVQ    DX, 8(SP)
        0x0162 00354 (interface_test.go:18)     PCDATA  $0, $4
        0x0162 00354 (interface_test.go:18)     CALL    runtime.writebarrierptr(SB)
        0x0167 00359 (interface_test.go:18)     MOVQ    ""..autotmp_13+64(SP), CX
        0x016c 00364 (interface_test.go:18)     JMP     194
        0x0171 00369 (interface_test.go:20)     MOVQ    120(SP), BP
        0x0176 00374 (interface_test.go:20)     ADDQ    $128, SP
        0x017d 00381 (interface_test.go:20)     RET
        0x017e 00382 (interface_test.go:20)     NOP
        0x017e 00382 (interface_test.go:15)     PCDATA  $0, $-1
        0x017e 00382 (interface_test.go:15)     CALL    runtime.morestack_noctxt(SB)
        0x0183 00387 (interface_test.go:15)     JMP     0

Closing as a dup of #19361 #18822 #19165 and other such bugs.

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@bradfitz @avinoamr @gopherbot