From 07751f4b582d17289dc19511e2f45d48021f827d Mon Sep 17 00:00:00 2001 From: Ian Lance Taylor Date: Mon, 27 Nov 2017 15:40:28 -0800 Subject: [PATCH] runtime: use private futexes on Linux By default futexes are permitted in shared memory regions, which requires the kernel to translate the memory address. Since our futexes are never in shared memory, set FUTEX_PRIVATE_FLAG, which makes futex operations slightly more efficient. Change-Id: I2a82365ed27d5cd8d53c5382ebaca1a720a80952 Reviewed-on: https://go-review.googlesource.com/80144 Reviewed-by: Brad Fitzpatrick Reviewed-by: David Crawshaw --- src/runtime/os_linux.go | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/src/runtime/os_linux.go b/src/runtime/os_linux.go index 2e442192cc..7231cf1226 100644 --- a/src/runtime/os_linux.go +++ b/src/runtime/os_linux.go @@ -24,8 +24,9 @@ func futex(addr unsafe.Pointer, op int32, val uint32, ts, addr2 unsafe.Pointer, // Futexsleep is allowed to wake up spuriously. const ( - _FUTEX_WAIT = 0 - _FUTEX_WAKE = 1 + _FUTEX_PRIVATE_FLAG = 128 + _FUTEX_WAIT_PRIVATE = 0 | _FUTEX_PRIVATE_FLAG + _FUTEX_WAKE_PRIVATE = 1 | _FUTEX_PRIVATE_FLAG ) // Atomically, @@ -42,7 +43,7 @@ func futexsleep(addr *uint32, val uint32, ns int64) { // here, and so can we: as it says a few lines up, // spurious wakeups are allowed. if ns < 0 { - futex(unsafe.Pointer(addr), _FUTEX_WAIT, val, nil, nil, 0) + futex(unsafe.Pointer(addr), _FUTEX_WAIT_PRIVATE, val, nil, nil, 0) return } @@ -59,13 +60,13 @@ func futexsleep(addr *uint32, val uint32, ns int64) { ts.tv_nsec = 0 ts.set_sec(int64(timediv(ns, 1000000000, (*int32)(unsafe.Pointer(&ts.tv_nsec))))) } - futex(unsafe.Pointer(addr), _FUTEX_WAIT, val, unsafe.Pointer(&ts), nil, 0) + futex(unsafe.Pointer(addr), _FUTEX_WAIT_PRIVATE, val, unsafe.Pointer(&ts), nil, 0) } // If any procs are sleeping on addr, wake up at most cnt. //go:nosplit func futexwakeup(addr *uint32, cnt uint32) { - ret := futex(unsafe.Pointer(addr), _FUTEX_WAKE, cnt, nil, nil, 0) + ret := futex(unsafe.Pointer(addr), _FUTEX_WAKE_PRIVATE, cnt, nil, nil, 0) if ret >= 0 { return } -- 2.50.0