runtime: rename ncpu to numCPUStartup

ncpu is the total logical CPU count at startup. It is never updated. For
#73193, we will start using updated CPU counts for updated GOMAXPROCS,
making the ncpu name a bit ambiguous. Change to a less ambiguous name.

While we're at it, give the OS specific lookup functions a common name,
so it can be used outside of osinit later.

For #73193.

Change-Id: I6a6a636cf21cc60de36b211f3c374080849fc667
Reviewed-on: https://go-review.googlesource.com/c/go/+/672277
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>

Author: prattmic

src/runtime/debug.go

@@ -40,7 +40,7 @@ func GOMAXPROCS(n int) int {
 // at process startup. Changes to operating system CPU allocation after
 // process startup are not reflected.
 func NumCPU() int {
-	return int(ncpu)
+	return int(numCPUStartup)
 }
 
 // NumCgoCall returns the number of cgo calls made by the current process.

src/runtime/heapdump.go

@@ -536,7 +536,7 @@ func dumpparams() {
 	dumpint(uint64(arenaEnd))
 	dumpstr(goarch.GOARCH)
 	dumpstr(buildVersion)
-	dumpint(uint64(ncpu))
+	dumpint(uint64(numCPUStartup))
 }
 
 func itab_callback(tab *itab) {

src/runtime/lock_spinbit.go

@@ -175,7 +175,7 @@ func lock2(l *mutex) {
 	// On uniprocessors, no point spinning.
 	// On multiprocessors, spin for mutexActiveSpinCount attempts.
 	spin := 0
-	if ncpu > 1 {
+	if numCPUStartup > 1 {
 		spin = mutexActiveSpinCount
 	}
 

src/runtime/mgc.go

@@ -727,10 +727,10 @@ func gcStart(trigger gcTrigger) {
 	systemstack(gcResetMarkState)
 
 	work.stwprocs, work.maxprocs = gomaxprocs, gomaxprocs
-	if work.stwprocs > ncpu {
-		// This is used to compute CPU time of the STW phases,
-		// so it can't be more than ncpu, even if GOMAXPROCS is.
-		work.stwprocs = ncpu
+	if work.stwprocs > numCPUStartup {
+		// This is used to compute CPU time of the STW phases, so it
+		// can't be more than the CPU count, even if GOMAXPROCS is.
+		work.stwprocs = numCPUStartup
 	}
 	work.heap0 = gcController.heapLive.Load()
 	work.pauseNS = 0

src/runtime/os3_solaris.go

@@ -137,7 +137,7 @@ func osinit() {
 	// before calling minit on m0.
 	asmcgocall(unsafe.Pointer(abi.FuncPCABI0(miniterrno)), unsafe.Pointer(&libc____errno))
 
-	ncpu = getncpu()
+	numCPUStartup = getCPUCount()
 	if physPageSize == 0 {
 		physPageSize = getPageSize()
 	}

src/runtime/os_aix.go

@@ -97,10 +97,14 @@ func osinit() {
 	// before calling minit on m0.
 	miniterrno()
 
-	ncpu = int32(sysconf(__SC_NPROCESSORS_ONLN))
+	numCPUStartup = getCPUCount()
 	physPageSize = sysconf(__SC_PAGE_SIZE)
 }
 
+func getCPUCount() int32 {
+	return int32(sysconf(__SC_NPROCESSORS_ONLN))
+}
+
 // newosproc0 is a version of newosproc that can be called before the runtime
 // is initialized.
 //

src/runtime/os_darwin.go

@@ -144,7 +144,7 @@ func osinit() {
 	// pthread_create delayed until end of goenvs so that we
 	// can look at the environment first.
 
-	ncpu = getncpu()
+	numCPUStartup = getCPUCount()
 	physPageSize = getPageSize()
 
 	osinit_hack()
@@ -168,7 +168,7 @@ const (
 	_HW_PAGESIZE = 7
 )
 
-func getncpu() int32 {
+func getCPUCount() int32 {
 	// Use sysctl to fetch hw.ncpu.
 	mib := [2]uint32{_CTL_HW, _HW_NCPU}
 	out := uint32(0)

src/runtime/os_dragonfly.go

@@ -78,7 +78,7 @@ const (
 
 var sigset_all = sigset{[4]uint32{^uint32(0), ^uint32(0), ^uint32(0), ^uint32(0)}}
 
-func getncpu() int32 {
+func getCPUCount() int32 {
 	mib := [2]uint32{_CTL_HW, _HW_NCPU}
 	out := uint32(0)
 	nout := unsafe.Sizeof(out)
@@ -174,7 +174,7 @@ func newosproc(mp *m) {
 }
 
 func osinit() {
-	ncpu = getncpu()
+	numCPUStartup = getCPUCount()
 	if physPageSize == 0 {
 		physPageSize = getPageSize()
 	}

src/runtime/os_freebsd.go

@@ -91,7 +91,7 @@ const (
 func cpuset_getaffinity(level int, which int, id int64, size int, mask *byte) int32
 
 //go:systemstack
-func getncpu() int32 {
+func getCPUCount() int32 {
 	// Use a large buffer for the CPU mask. We're on the system
 	// stack, so this is fine, and we can't allocate memory for a
 	// dynamically-sized buffer at this point.
@@ -276,7 +276,7 @@ func libpreinit() {
 }
 
 func osinit() {
-	ncpu = getncpu()
+	numCPUStartup = getCPUCount()
 	if physPageSize == 0 {
 		physPageSize = getPageSize()
 	}

src/runtime/os_freebsd_arm.go

@@ -28,8 +28,9 @@ func checkgoarm() {
 		exit(1)
 	}
 
-	// osinit not called yet, so ncpu not set: must use getncpu directly.
-	if getncpu() > 1 && goarm < 7 {
+	// osinit not called yet, so numCPUStartup not set: must use
+	// getCPUCount directly.
+	if getCPUCount() > 1 && goarm < 7 {
 		print("runtime: this system has multiple CPUs and must use\n")
 		print("atomic synchronization instructions. Recompile using GOARM=7.\n")
 		exit(1)