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| author | Shenghou Ma <minux@golang.org> | 2019-09-30 09:44:37 -0400 |
|---|---|---|
| committer | Alexander Rakoczy <alex@golang.org> | 2019-10-09 20:10:40 +0000 |
| commit | 81d995d9eec249864b8dbb541bec3e40da860c71 (patch) | |
| tree | bf77bbb3c2c4f25590b421168621cf4b733f397f | |
| parent | 842a1e78c9533254d8d82a5571bdf24c0168beb3 (diff) | |
| download | go-81d995d9eec249864b8dbb541bec3e40da860c71.tar.gz go-81d995d9eec249864b8dbb541bec3e40da860c71.zip | |
[release-branch.go1.13] runtime: fix darwin syscall performance regression
While understanding why syscall.Read is 2x slower on darwin/amd64, I found
out that, contrary to popular belief, the slowdown is not due to the migration
to use libSystem.dylib instead of direct SYSCALLs, i.e., CL 141639 (and #17490),
but due to a subtle change introduced in CL 141639.
Previously, syscall.Read used syscall.Syscall(SYS_READ), whose preamble called
runtime.entersyscall, but after CL 141639, syscall.Read changes to call
runtime.syscall_syscall instead, which in turn calls runtime.entersyscallblock
instead of runtime.entersyscall. And the entire 2x slow down can be attributed
to this change.
I think this is unnecessary as even though syscalls like Read might block, it
does not always block, so there is no need to handoff P proactively for each
Read. Additionally, we have been fine with not handing off P for each Read
prior to Go 1.12, so we probably don't need to change it. This changes restores
the pre-Go 1.12 behavior, where syscall preamble uses runtime.entersyscall,
and we rely on sysmon to take P back from g blocked in syscalls.
Updates #34712
Change-Id: If76e97b5a7040cf1c10380a567c4f5baec3121ba
Reviewed-on: https://go-review.googlesource.com/c/go/+/197938
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
(cherry picked from commit c1635ad8f0bb9fbe5bfbf0a633c78a03930758c4)
Reviewed-on: https://go-review.googlesource.com/c/go/+/200103
Run-TryBot: Alexander Rakoczy <alex@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
| -rw-r--r-- | src/runtime/sys_darwin.go | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/src/runtime/sys_darwin.go b/src/runtime/sys_darwin.go index 376f76dbc5..a630d53a6e 100644 --- a/src/runtime/sys_darwin.go +++ b/src/runtime/sys_darwin.go @@ -60,7 +60,7 @@ func libcCall(fn, arg unsafe.Pointer) int32 { //go:nosplit //go:cgo_unsafe_args func syscall_syscall(fn, a1, a2, a3 uintptr) (r1, r2, err uintptr) { - entersyscallblock() + entersyscall() libcCall(unsafe.Pointer(funcPC(syscall)), unsafe.Pointer(&fn)) exitsyscall() return @@ -71,7 +71,7 @@ func syscall() //go:nosplit //go:cgo_unsafe_args func syscall_syscall6(fn, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr) { - entersyscallblock() + entersyscall() libcCall(unsafe.Pointer(funcPC(syscall6)), unsafe.Pointer(&fn)) exitsyscall() return @@ -82,7 +82,7 @@ func syscall6() //go:nosplit //go:cgo_unsafe_args func syscall_syscall6X(fn, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr) { - entersyscallblock() + entersyscall() libcCall(unsafe.Pointer(funcPC(syscall6X)), unsafe.Pointer(&fn)) exitsyscall() return @@ -93,7 +93,7 @@ func syscall6X() //go:nosplit //go:cgo_unsafe_args func syscall_syscallPtr(fn, a1, a2, a3 uintptr) (r1, r2, err uintptr) { - entersyscallblock() + entersyscall() libcCall(unsafe.Pointer(funcPC(syscallPtr)), unsafe.Pointer(&fn)) exitsyscall() return |