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runtime: use private futexes on Linux

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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 <bradfitz@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
This commit is contained in:
Ian Lance Taylor 2017-11-27 15:40:28 -08:00
parent ebd4950e3b
commit 07751f4b58
1 changed files with 6 additions and 5 deletions
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11
src/runtime/os_linux.go
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@ -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
}