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gvisor/pkg/sync/goyield_unsafe.go

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Improve sync.SeqCount performance. - Make sync.SeqCountEpoch not a struct. This allows sync.SeqCount.BeginRead() to be inlined. - Mark sync.SeqAtomicLoad<T> nosplit to mitigate the Go compiler's refusal to inline it. (Best I could get was "cost 92 exceeds budget 80".) - Use runtime-guided spinning in SeqCount.BeginRead(). Benchmarks: name old time/op new time/op delta pkg:pkg/sync/sync goos:linux goarch:amd64 SeqCountWriteUncontended-12 8.24ns ± 0% 11.40ns ± 0% +38.35% (p=0.000 n=10+10) SeqCountReadUncontended-12 0.33ns ± 0% 0.14ns ± 3% -57.77% (p=0.000 n=7+8) pkg:pkg/sync/seqatomictest/seqatomic goos:linux goarch:amd64 SeqAtomicLoadIntUncontended-12 0.64ns ± 1% 0.41ns ± 1% -36.40% (p=0.000 n=10+8) SeqAtomicTryLoadIntUncontended-12 0.18ns ± 4% 0.18ns ± 1% ~ (p=0.206 n=10+8) AtomicValueLoadIntUncontended-12 0.27ns ± 3% 0.27ns ± 0% -1.77% (p=0.000 n=10+8) (atomic.Value.Load is, of course, inlined. We would expect an uncontended inline SeqAtomicLoad<int> to perform identically to SeqAtomicTryLoad<int>.) The "regression" in BenchmarkSeqCountWriteUncontended, despite this CL changing nothing in that path, is attributed to microarchitectural subtlety; the benchmark loop is unchanged except for its address: Before this CL: :0 0x4e62d1 48ffc2 INCQ DX :0 0x4e62d4 48399110010000 CMPQ DX, 0x110(CX) :0 0x4e62db 7e26 JLE 0x4e6303 :0 0x4e62dd 90 NOPL :0 0x4e62de bb01000000 MOVL $0x1, BX :0 0x4e62e3 f00fc118 LOCK XADDL BX, 0(AX) :0 0x4e62e7 ffc3 INCL BX :0 0x4e62e9 0fbae300 BTL $0x0, BX :0 0x4e62ed 733a JAE 0x4e6329 :0 0x4e62ef 90 NOPL :0 0x4e62f0 bb01000000 MOVL $0x1, BX :0 0x4e62f5 f00fc118 LOCK XADDL BX, 0(AX) :0 0x4e62f9 ffc3 INCL BX :0 0x4e62fb 0fbae300 BTL $0x0, BX :0 0x4e62ff 73d0 JAE 0x4e62d1 After this CL: :0 0x4e6361 48ffc2 INCQ DX :0 0x4e6364 48399110010000 CMPQ DX, 0x110(CX) :0 0x4e636b 7e26 JLE 0x4e6393 :0 0x4e636d 90 NOPL :0 0x4e636e bb01000000 MOVL $0x1, BX :0 0x4e6373 f00fc118 LOCK XADDL BX, 0(AX) :0 0x4e6377 ffc3 INCL BX :0 0x4e6379 0fbae300 BTL $0x0, BX :0 0x4e637d 733a JAE 0x4e63b9 :0 0x4e637f 90 NOPL :0 0x4e6380 bb01000000 MOVL $0x1, BX :0 0x4e6385 f00fc118 LOCK XADDL BX, 0(AX) :0 0x4e6389 ffc3 INCL BX :0 0x4e638b 0fbae300 BTL $0x0, BX :0 0x4e638f 73d0 JAE 0x4e6361 PiperOrigin-RevId: 329754148
2020-09-02 18:35:18 +00:00
// Copyright 2020 The gVisor Authors.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
Fix link against runtime.goyield. This function does not exist in Go 1.13. We need to add an adaptor to build against Go 1.13, which is the default Ubuntu version. PiperOrigin-RevId: 343929132
2020-11-23 22:25:37 +00:00
// +build go1.14
Bump build constraints to Go 1.18 These are bumped to allow early testing of Go 1.17. Use will be audited closer to the 1.17 release. PiperOrigin-RevId: 358278615
2021-02-18 23:29:15 +00:00
// +build !go1.18
Improve sync.SeqCount performance. - Make sync.SeqCountEpoch not a struct. This allows sync.SeqCount.BeginRead() to be inlined. - Mark sync.SeqAtomicLoad<T> nosplit to mitigate the Go compiler's refusal to inline it. (Best I could get was "cost 92 exceeds budget 80".) - Use runtime-guided spinning in SeqCount.BeginRead(). Benchmarks: name old time/op new time/op delta pkg:pkg/sync/sync goos:linux goarch:amd64 SeqCountWriteUncontended-12 8.24ns ± 0% 11.40ns ± 0% +38.35% (p=0.000 n=10+10) SeqCountReadUncontended-12 0.33ns ± 0% 0.14ns ± 3% -57.77% (p=0.000 n=7+8) pkg:pkg/sync/seqatomictest/seqatomic goos:linux goarch:amd64 SeqAtomicLoadIntUncontended-12 0.64ns ± 1% 0.41ns ± 1% -36.40% (p=0.000 n=10+8) SeqAtomicTryLoadIntUncontended-12 0.18ns ± 4% 0.18ns ± 1% ~ (p=0.206 n=10+8) AtomicValueLoadIntUncontended-12 0.27ns ± 3% 0.27ns ± 0% -1.77% (p=0.000 n=10+8) (atomic.Value.Load is, of course, inlined. We would expect an uncontended inline SeqAtomicLoad<int> to perform identically to SeqAtomicTryLoad<int>.) The "regression" in BenchmarkSeqCountWriteUncontended, despite this CL changing nothing in that path, is attributed to microarchitectural subtlety; the benchmark loop is unchanged except for its address: Before this CL: :0 0x4e62d1 48ffc2 INCQ DX :0 0x4e62d4 48399110010000 CMPQ DX, 0x110(CX) :0 0x4e62db 7e26 JLE 0x4e6303 :0 0x4e62dd 90 NOPL :0 0x4e62de bb01000000 MOVL $0x1, BX :0 0x4e62e3 f00fc118 LOCK XADDL BX, 0(AX) :0 0x4e62e7 ffc3 INCL BX :0 0x4e62e9 0fbae300 BTL $0x0, BX :0 0x4e62ed 733a JAE 0x4e6329 :0 0x4e62ef 90 NOPL :0 0x4e62f0 bb01000000 MOVL $0x1, BX :0 0x4e62f5 f00fc118 LOCK XADDL BX, 0(AX) :0 0x4e62f9 ffc3 INCL BX :0 0x4e62fb 0fbae300 BTL $0x0, BX :0 0x4e62ff 73d0 JAE 0x4e62d1 After this CL: :0 0x4e6361 48ffc2 INCQ DX :0 0x4e6364 48399110010000 CMPQ DX, 0x110(CX) :0 0x4e636b 7e26 JLE 0x4e6393 :0 0x4e636d 90 NOPL :0 0x4e636e bb01000000 MOVL $0x1, BX :0 0x4e6373 f00fc118 LOCK XADDL BX, 0(AX) :0 0x4e6377 ffc3 INCL BX :0 0x4e6379 0fbae300 BTL $0x0, BX :0 0x4e637d 733a JAE 0x4e63b9 :0 0x4e637f 90 NOPL :0 0x4e6380 bb01000000 MOVL $0x1, BX :0 0x4e6385 f00fc118 LOCK XADDL BX, 0(AX) :0 0x4e6389 ffc3 INCL BX :0 0x4e638b 0fbae300 BTL $0x0, BX :0 0x4e638f 73d0 JAE 0x4e6361 PiperOrigin-RevId: 329754148
2020-09-02 18:35:18 +00:00
// Check go:linkname function signatures when updating Go version.
package sync
import (
_ "unsafe" // for go:linkname
)
//go:linkname goyield runtime.goyield
func goyield()