runtime: fast clock_gettime on FreeBSD, split getHPETTimecounter

Call only initHPETTimecounter on the system stack.
Use O_CLOEXEC flag when opening the HPET device.

FreeBSD 12.3-RELEASE-p2, AMD FX-8300
paulzhol@relic:~/go/src/time % ~/gocode/bin/benchcmp old_hpet.txt new_hpet.txt
benchcmp is deprecated in favor of benchstat: https://pkg.go.dev/golang.org/x/perf/cmd/benchstat
benchmark                   old ns/op     new ns/op     delta
BenchmarkNow-8              1420          1397          -1.62%
BenchmarkNowUnixNano-8      1421          1404          -1.20%
BenchmarkNowUnixMilli-8     1423          1405          -1.26%
BenchmarkNowUnixMicro-8     1423          1404          -1.34%

Update #50947

Change-Id: I553b5427fb0b86d7e070af4516b36326bc0aaf00
Reviewed-on: https://go-review.googlesource.com/c/go/+/391856
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

diff --git a/src/runtime/vdso_freebsd_x86.go b/src/runtime/vdso_freebsd_x86.go
index 5324a3d4cb3206390a33826cf72839e174a6c92c..66d1c654885ab8616d5d94b925599a816e35f6a4 100644 (file)
--- a/src/runtime/vdso_freebsd_x86.go
+++ b/src/runtime/vdso_freebsd_x86.go
@@ -34,10 +34,8 @@ func (th *vdsoTimehands) getTSCTimecounter() uint32 {
        return uint32(tsc)
 }
 
-//go:systemstack
+//go:nosplit
 func (th *vdsoTimehands) getHPETTimecounter() (uint32, bool) {
-       const digits = "0123456789"
-
        idx := int(th.x86_hpet_idx)
        if idx >= len(hpetDevMap) {
                return 0, false
@@ -45,25 +43,7 @@ func (th *vdsoTimehands) getHPETTimecounter() (uint32, bool) {
 
        p := atomic.Loaduintptr(&hpetDevMap[idx])
        if p == 0 {
-               var devPath [len(hpetDevPath)]byte
-               copy(devPath[:], hpetDevPath)
-               devPath[9] = digits[idx]
-
-               fd := open(&devPath[0], 0 /* O_RDONLY */, 0)
-               if fd < 0 {
-                       atomic.Casuintptr(&hpetDevMap[idx], 0, ^uintptr(0))
-                       return 0, false
-               }
-
-               addr, mmapErr := mmap(nil, physPageSize, _PROT_READ, _MAP_SHARED, fd, 0)
-               closefd(fd)
-               newP := uintptr(addr)
-               if mmapErr != 0 {
-                       newP = ^uintptr(0)
-               }
-               if !atomic.Casuintptr(&hpetDevMap[idx], 0, newP) && mmapErr == 0 {
-                       munmap(addr, physPageSize)
-               }
+               systemstack(func() { initHPETTimecounter(idx) })
                p = atomic.Loaduintptr(&hpetDevMap[idx])
        }
        if p == ^uintptr(0) {
@@ -72,20 +52,38 @@ func (th *vdsoTimehands) getHPETTimecounter() (uint32, bool) {
        return *(*uint32)(unsafe.Pointer(p + _HPET_MAIN_COUNTER)), true
 }
 
+//go:systemstack
+func initHPETTimecounter(idx int) {
+       const digits = "0123456789"
+
+       var devPath [len(hpetDevPath)]byte
+       copy(devPath[:], hpetDevPath)
+       devPath[9] = digits[idx]
+
+       fd := open(&devPath[0], 0 /* O_RDONLY */ |_O_CLOEXEC, 0)
+       if fd < 0 {
+               atomic.Casuintptr(&hpetDevMap[idx], 0, ^uintptr(0))
+               return
+       }
+
+       addr, mmapErr := mmap(nil, physPageSize, _PROT_READ, _MAP_SHARED, fd, 0)
+       closefd(fd)
+       newP := uintptr(addr)
+       if mmapErr != 0 {
+               newP = ^uintptr(0)
+       }
+       if !atomic.Casuintptr(&hpetDevMap[idx], 0, newP) && mmapErr == 0 {
+               munmap(addr, physPageSize)
+       }
+}
+
 //go:nosplit
 func (th *vdsoTimehands) getTimecounter() (uint32, bool) {
        switch th.algo {
        case _VDSO_TH_ALGO_X86_TSC:
                return th.getTSCTimecounter(), true
        case _VDSO_TH_ALGO_X86_HPET:
-               var (
-                       tc uint32
-                       ok bool
-               )
-               systemstack(func() {
-                       tc, ok = th.getHPETTimecounter()
-               })
-               return tc, ok
+               return th.getHPETTimecounter()
        default:
                return 0, false
        }