| commit | c1635ad8f0bb9fbe5bfbf0a633c78a03930758c4 | [log] [tgz] |
|---|---|---|
| author | Shenghou Ma <minux@golang.org> | Mon Sep 30 09:44:37 2019 -0400 |
| committer | Minux Ma <minux@golang.org> | Tue Oct 01 04:04:40 2019 +0000 |
| tree | 553831168b444b95b703693152dfd0e1b73add1b | |
| parent | e617141b0b35f14f5fe9113febcc84a2b0ecb642 [diff] |
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. 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>
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