Ejemplo n.º 1
0
func RunSchedLocalQueueEmptyTest(iters int) {
	// Test that runq is not spuriously reported as empty.
	// Runq emptiness affects scheduling decisions and spurious emptiness
	// can lead to underutilization (both runnable Gs and idle Ps coexist
	// for arbitrary long time).
	done := make(chan bool, 1)
	p := new(p)
	gs := make([]g, 2)
	ready := new(uint32)
	for i := 0; i < iters; i++ {
		*ready = 0
		next0 := (i & 1) == 0
		next1 := (i & 2) == 0
		runqput(p, &gs[0], next0)
		go func() {
			for atomic.Xadd(ready, 1); atomic.Load(ready) != 2; {
			}
			if runqempty(p) {
				println("next:", next0, next1)
				throw("queue is empty")
			}
			done <- true
		}()
		for atomic.Xadd(ready, 1); atomic.Load(ready) != 2; {
		}
		runqput(p, &gs[1], next1)
		runqget(p)
		<-done
		runqget(p)
	}
}
Ejemplo n.º 2
0
Archivo: sema.go Proyecto: danny8002/go
func semrelease(addr *uint32) {
	root := semroot(addr)
	atomic.Xadd(addr, 1)

	// Easy case: no waiters?
	// This check must happen after the xadd, to avoid a missed wakeup
	// (see loop in semacquire).
	if atomic.Load(&root.nwait) == 0 {
		return
	}

	// Harder case: search for a waiter and wake it.
	lock(&root.lock)
	if atomic.Load(&root.nwait) == 0 {
		// The count is already consumed by another goroutine,
		// so no need to wake up another goroutine.
		unlock(&root.lock)
		return
	}
	s := root.head
	for ; s != nil; s = s.next {
		if s.elem == unsafe.Pointer(addr) {
			atomic.Xadd(&root.nwait, -1)
			root.dequeue(s)
			break
		}
	}
	unlock(&root.lock)
	if s != nil {
		if s.releasetime != 0 {
			s.releasetime = cputicks()
		}
		goready(s.g, 4)
	}
}
Ejemplo n.º 3
0
Archivo: sema.go Proyecto: achanda/go
// Called from runtime.
func semacquire(addr *uint32, profile semaProfileFlags) {
	gp := getg()
	if gp != gp.m.curg {
		throw("semacquire not on the G stack")
	}

	// Easy case.
	if cansemacquire(addr) {
		return
	}

	// Harder case:
	//	increment waiter count
	//	try cansemacquire one more time, return if succeeded
	//	enqueue itself as a waiter
	//	sleep
	//	(waiter descriptor is dequeued by signaler)
	s := acquireSudog()
	root := semroot(addr)
	t0 := int64(0)
	s.releasetime = 0
	s.acquiretime = 0
	if profile&semaBlockProfile != 0 && blockprofilerate > 0 {
		t0 = cputicks()
		s.releasetime = -1
	}
	if profile&semaMutexProfile != 0 && mutexprofilerate > 0 {
		if t0 == 0 {
			t0 = cputicks()
		}
		s.acquiretime = t0
	}
	for {
		lock(&root.lock)
		// Add ourselves to nwait to disable "easy case" in semrelease.
		atomic.Xadd(&root.nwait, 1)
		// Check cansemacquire to avoid missed wakeup.
		if cansemacquire(addr) {
			atomic.Xadd(&root.nwait, -1)
			unlock(&root.lock)
			break
		}
		// Any semrelease after the cansemacquire knows we're waiting
		// (we set nwait above), so go to sleep.
		root.queue(addr, s)
		goparkunlock(&root.lock, "semacquire", traceEvGoBlockSync, 4)
		if cansemacquire(addr) {
			break
		}
	}
	if s.releasetime > 0 {
		blockevent(s.releasetime-t0, 3)
	}
	releaseSudog(s)
}
Ejemplo n.º 4
0
// Get a full work buffer off the work.full list.
// If nothing is available wait until all the other gc helpers have
// finished and then return nil.
// getfull acts as a barrier for work.nproc helpers. As long as one
// gchelper is actively marking objects it
// may create a workbuffer that the other helpers can work on.
// The for loop either exits when a work buffer is found
// or when _all_ of the work.nproc GC helpers are in the loop
// looking for work and thus not capable of creating new work.
// This is in fact the termination condition for the STW mark
// phase.
//go:nowritebarrier
func getfull(entry int) *workbuf {
	b := (*workbuf)(lfstackpop(&work.full))
	if b != nil {
		b.logget(entry)
		b.checknonempty()
		return b
	}

	incnwait := atomic.Xadd(&work.nwait, +1)
	if incnwait > work.nproc {
		println("runtime: work.nwait=", incnwait, "work.nproc=", work.nproc)
		throw("work.nwait > work.nproc")
	}
	for i := 0; ; i++ {
		if work.full != 0 {
			decnwait := atomic.Xadd(&work.nwait, -1)
			if decnwait == work.nproc {
				println("runtime: work.nwait=", decnwait, "work.nproc=", work.nproc)
				throw("work.nwait > work.nproc")
			}
			b = (*workbuf)(lfstackpop(&work.full))
			if b != nil {
				b.logget(entry)
				b.checknonempty()
				return b
			}
			incnwait := atomic.Xadd(&work.nwait, +1)
			if incnwait > work.nproc {
				println("runtime: work.nwait=", incnwait, "work.nproc=", work.nproc)
				throw("work.nwait > work.nproc")
			}
		}
		if work.nwait == work.nproc && work.markrootNext >= work.markrootJobs {
			return nil
		}
		_g_ := getg()
		if i < 10 {
			_g_.m.gcstats.nprocyield++
			procyield(20)
		} else if i < 20 {
			_g_.m.gcstats.nosyield++
			osyield()
		} else {
			_g_.m.gcstats.nsleep++
			usleep(100)
		}
	}
}
Ejemplo n.º 5
0
// sweeps one span
// returns number of pages returned to heap, or ^uintptr(0) if there is nothing to sweep
//go:nowritebarrier
func sweepone() uintptr {
	_g_ := getg()

	// increment locks to ensure that the goroutine is not preempted
	// in the middle of sweep thus leaving the span in an inconsistent state for next GC
	_g_.m.locks++
	sg := mheap_.sweepgen
	for {
		idx := atomic.Xadd(&sweep.spanidx, 1) - 1
		if idx >= uint32(len(work.spans)) {
			mheap_.sweepdone = 1
			_g_.m.locks--
			return ^uintptr(0)
		}
		s := work.spans[idx]
		if s.state != mSpanInUse {
			s.sweepgen = sg
			continue
		}
		if s.sweepgen != sg-2 || !atomic.Cas(&s.sweepgen, sg-2, sg-1) {
			continue
		}
		npages := s.npages
		if !s.sweep(false) {
			npages = 0
		}
		_g_.m.locks--
		return npages
	}
}
Ejemplo n.º 6
0
// sweeps one span
// returns number of pages returned to heap, or ^uintptr(0) if there is nothing to sweep
//go:nowritebarrier
func sweepone() uintptr {
	_g_ := getg()

	// increment locks to ensure that the goroutine is not preempted
	// in the middle of sweep thus leaving the span in an inconsistent state for next GC
	_g_.m.locks++
	sg := mheap_.sweepgen
	for {
		idx := atomic.Xadd(&sweep.spanidx, 1) - 1
		if idx >= uint32(len(work.spans)) {
			mheap_.sweepdone = 1
			_g_.m.locks--
			if debug.gcpacertrace > 0 && idx == uint32(len(work.spans)) {
				print("pacer: sweep done at heap size ", memstats.heap_live>>20, "MB; allocated ", mheap_.spanBytesAlloc>>20, "MB of spans; swept ", mheap_.pagesSwept, " pages at ", mheap_.sweepPagesPerByte, " pages/byte\n")
			}
			return ^uintptr(0)
		}
		s := work.spans[idx]
		if s.state != mSpanInUse {
			s.sweepgen = sg
			continue
		}
		if s.sweepgen != sg-2 || !atomic.Cas(&s.sweepgen, sg-2, sg-1) {
			continue
		}
		npages := s.npages
		if !s.sweep(false) {
			npages = 0
		}
		_g_.m.locks--
		return npages
	}
}
Ejemplo n.º 7
0
Archivo: proc.go Proyecto: kraj/gcc
// lockextra locks the extra list and returns the list head.
// The caller must unlock the list by storing a new list head
// to extram. If nilokay is true, then lockextra will
// return a nil list head if that's what it finds. If nilokay is false,
// lockextra will keep waiting until the list head is no longer nil.
//go:nosplit
func lockextra(nilokay bool) *m {
	const locked = 1

	incr := false
	for {
		old := atomic.Loaduintptr(&extram)
		if old == locked {
			yield := osyield
			yield()
			continue
		}
		if old == 0 && !nilokay {
			if !incr {
				// Add 1 to the number of threads
				// waiting for an M.
				// This is cleared by newextram.
				atomic.Xadd(&extraMWaiters, 1)
				incr = true
			}
			usleep(1)
			continue
		}
		if atomic.Casuintptr(&extram, old, locked) {
			return (*m)(unsafe.Pointer(old))
		}
		yield := osyield
		yield()
		continue
	}
}
Ejemplo n.º 8
0
// pop removes and returns a span from buffer b, or nil if b is empty.
// pop is safe to call concurrently with other pop operations, but NOT
// to call concurrently with push.
func (b *gcSweepBuf) pop() *mspan {
	cursor := atomic.Xadd(&b.index, -1)
	if int32(cursor) < 0 {
		atomic.Xadd(&b.index, +1)
		return nil
	}

	// There are no concurrent spine or block modifications during
	// pop, so we can omit the atomics.
	top, bottom := cursor/gcSweepBlockEntries, cursor%gcSweepBlockEntries
	blockp := (**gcSweepBlock)(add(b.spine, sys.PtrSize*uintptr(top)))
	block := *blockp
	s := block.spans[bottom]
	// Clear the pointer for block(i).
	block.spans[bottom] = nil
	return s
}
Ejemplo n.º 9
0
// gcDrainN blackens grey objects until it has performed roughly
// scanWork units of scan work or the G is preempted. This is
// best-effort, so it may perform less work if it fails to get a work
// buffer. Otherwise, it will perform at least n units of work, but
// may perform more because scanning is always done in whole object
// increments. It returns the amount of scan work performed.
//
// The caller goroutine must be in a preemptible state (e.g.,
// _Gwaiting) to prevent deadlocks during stack scanning. As a
// consequence, this must be called on the system stack.
//
//go:nowritebarrier
//go:systemstack
func gcDrainN(gcw *gcWork, scanWork int64) int64 {
	if !writeBarrier.needed {
		throw("gcDrainN phase incorrect")
	}

	// There may already be scan work on the gcw, which we don't
	// want to claim was done by this call.
	workFlushed := -gcw.scanWork

	gp := getg().m.curg
	for !gp.preempt && workFlushed+gcw.scanWork < scanWork {
		// See gcDrain comment.
		if work.full == 0 {
			gcw.balance()
		}

		// This might be a good place to add prefetch code...
		// if(wbuf.nobj > 4) {
		//         PREFETCH(wbuf->obj[wbuf.nobj - 3];
		//  }
		//
		b := gcw.tryGetFast()
		if b == 0 {
			b = gcw.tryGet()
		}

		if b == 0 {
			// Try to do a root job.
			//
			// TODO: Assists should get credit for this
			// work.
			if work.markrootNext < work.markrootJobs {
				job := atomic.Xadd(&work.markrootNext, +1) - 1
				if job < work.markrootJobs {
					markroot(gcw, job)
					continue
				}
			}
			// No heap or root jobs.
			break
		}
		scanobject(b, gcw)

		// Flush background scan work credit.
		if gcw.scanWork >= gcCreditSlack {
			atomic.Xaddint64(&gcController.scanWork, gcw.scanWork)
			workFlushed += gcw.scanWork
			gcw.scanWork = 0
		}
	}

	// Unlike gcDrain, there's no need to flush remaining work
	// here because this never flushes to bgScanCredit and
	// gcw.dispose will flush any remaining work to scanWork.

	return workFlushed + gcw.scanWork
}
Ejemplo n.º 10
0
Archivo: sema.go Proyecto: achanda/go
func semrelease(addr *uint32) {
	root := semroot(addr)
	atomic.Xadd(addr, 1)

	// Easy case: no waiters?
	// This check must happen after the xadd, to avoid a missed wakeup
	// (see loop in semacquire).
	if atomic.Load(&root.nwait) == 0 {
		return
	}

	// Harder case: search for a waiter and wake it.
	lock(&root.lock)
	if atomic.Load(&root.nwait) == 0 {
		// The count is already consumed by another goroutine,
		// so no need to wake up another goroutine.
		unlock(&root.lock)
		return
	}
	s := root.head
	for ; s != nil; s = s.next {
		if s.elem == unsafe.Pointer(addr) {
			atomic.Xadd(&root.nwait, -1)
			root.dequeue(s)
			break
		}
	}
	if s != nil {
		if s.acquiretime != 0 {
			t0 := cputicks()
			for x := root.head; x != nil; x = x.next {
				if x.elem == unsafe.Pointer(addr) {
					x.acquiretime = t0
				}
			}
			mutexevent(t0-s.acquiretime, 3)
		}
	}
	unlock(&root.lock)
	if s != nil { // May be slow, so unlock first
		readyWithTime(s, 5)
	}
}
Ejemplo n.º 11
0
//go:nosplit
func semawakeup(mp *m) {
	atomic.Xadd(&mp.waitsemacount, 1)
	ret := thrwakeup(uintptr(unsafe.Pointer(&mp.waitsemacount)), 1)
	if ret != 0 && ret != _ESRCH {
		// semawakeup can be called on signal stack.
		systemstack(func() {
			print("thrwakeup addr=", &mp.waitsemacount, " sem=", mp.waitsemacount, " ret=", ret, "\n")
		})
	}
}
Ejemplo n.º 12
0
//go:nosplit
func semawakeup(mp *m) {
	atomic.Xadd(&mp.waitsemacount, 1)
	// From NetBSD's _lwp_unpark(2) manual:
	// "If the target LWP is not currently waiting, it will return
	// immediately upon the next call to _lwp_park()."
	ret := lwp_unpark(int32(mp.procid), unsafe.Pointer(&mp.waitsemacount))
	if ret != 0 && ret != _ESRCH {
		// semawakeup can be called on signal stack.
		systemstack(func() {
			print("thrwakeup addr=", &mp.waitsemacount, " sem=", mp.waitsemacount, " ret=", ret, "\n")
		})
	}
}
Ejemplo n.º 13
0
Archivo: panic.go Proyecto: kraj/gcc
func dopanic(unused int) {
	gp := getg()
	if gp.sig != 0 {
		signame := signame(gp.sig)
		if signame != "" {
			print("[signal ", signame)
		} else {
			print("[signal ", hex(gp.sig))
		}
		print(" code=", hex(gp.sigcode0), " addr=", hex(gp.sigcode1), " pc=", hex(gp.sigpc), "]\n")
	}

	level, all, docrash := gotraceback()
	_g_ := getg()
	if level > 0 {
		if gp != gp.m.curg {
			all = true
		}
		if gp != gp.m.g0 {
			print("\n")
			goroutineheader(gp)
			traceback(0)
		} else if level >= 2 || _g_.m.throwing > 0 {
			print("\nruntime stack:\n")
			traceback(0)
		}
		if !didothers && all {
			didothers = true
			tracebackothers(gp)
		}
	}
	unlock(&paniclk)

	if atomic.Xadd(&panicking, -1) != 0 {
		// Some other m is panicking too.
		// Let it print what it needs to print.
		// Wait forever without chewing up cpu.
		// It will exit when it's done.
		lock(&deadlock)
		lock(&deadlock)
	}

	if docrash {
		crash()
	}

	exit(2)
}
Ejemplo n.º 14
0
Archivo: panic.go Proyecto: kraj/gcc
func startpanic() {
	_g_ := getg()
	// Uncomment when mheap_ is in Go.
	// if mheap_.cachealloc.size == 0 { // very early
	//	print("runtime: panic before malloc heap initialized\n")
	//	_g_.m.mallocing = 1 // tell rest of panic not to try to malloc
	// } else
	if _g_.m.mcache == nil { // can happen if called from signal handler or throw
		_g_.m.mcache = allocmcache()
	}

	switch _g_.m.dying {
	case 0:
		_g_.m.dying = 1
		_g_.writebuf = nil
		atomic.Xadd(&panicking, 1)
		lock(&paniclk)
		if debug.schedtrace > 0 || debug.scheddetail > 0 {
			schedtrace(true)
		}
		freezetheworld()
		return
	case 1:
		// Something failed while panicing, probably the print of the
		// argument to panic().  Just print a stack trace and exit.
		_g_.m.dying = 2
		print("panic during panic\n")
		dopanic(0)
		exit(3)
		fallthrough
	case 2:
		// This is a genuine bug in the runtime, we couldn't even
		// print the stack trace successfully.
		_g_.m.dying = 3
		print("stack trace unavailable\n")
		exit(4)
		fallthrough
	default:
		// Can't even print!  Just exit.
		exit(5)
	}
}
Ejemplo n.º 15
0
func queuefinalizer(p unsafe.Pointer, fn *funcval, nret uintptr, fint *_type, ot *ptrtype) {
	lock(&finlock)
	if finq == nil || finq.cnt == uint32(len(finq.fin)) {
		if finc == nil {
			finc = (*finblock)(persistentalloc(_FinBlockSize, 0, &memstats.gc_sys))
			finc.alllink = allfin
			allfin = finc
			if finptrmask[0] == 0 {
				// Build pointer mask for Finalizer array in block.
				// Check assumptions made in finalizer1 array above.
				if (unsafe.Sizeof(finalizer{}) != 5*sys.PtrSize ||
					unsafe.Offsetof(finalizer{}.fn) != 0 ||
					unsafe.Offsetof(finalizer{}.arg) != sys.PtrSize ||
					unsafe.Offsetof(finalizer{}.nret) != 2*sys.PtrSize ||
					unsafe.Offsetof(finalizer{}.fint) != 3*sys.PtrSize ||
					unsafe.Offsetof(finalizer{}.ot) != 4*sys.PtrSize) {
					throw("finalizer out of sync")
				}
				for i := range finptrmask {
					finptrmask[i] = finalizer1[i%len(finalizer1)]
				}
			}
		}
		block := finc
		finc = block.next
		block.next = finq
		finq = block
	}
	f := &finq.fin[finq.cnt]
	atomic.Xadd(&finq.cnt, +1) // Sync with markroots
	f.fn = fn
	f.nret = nret
	f.fint = fint
	f.ot = ot
	f.arg = p
	fingwake = true
	unlock(&finlock)
}
Ejemplo n.º 16
0
// gcAssistAlloc1 is the part of gcAssistAlloc that runs on the system
// stack. This is a separate function to make it easier to see that
// we're not capturing anything from the user stack, since the user
// stack may move while we're in this function.
//
// gcAssistAlloc1 indicates whether this assist completed the mark
// phase by setting gp.param to non-nil. This can't be communicated on
// the stack since it may move.
//
//go:systemstack
func gcAssistAlloc1(gp *g, scanWork int64) {
	// Clear the flag indicating that this assist completed the
	// mark phase.
	gp.param = nil

	if atomic.Load(&gcBlackenEnabled) == 0 {
		// The gcBlackenEnabled check in malloc races with the
		// store that clears it but an atomic check in every malloc
		// would be a performance hit.
		// Instead we recheck it here on the non-preemptable system
		// stack to determine if we should preform an assist.

		// GC is done, so ignore any remaining debt.
		gp.gcAssistBytes = 0
		return
	}
	// Track time spent in this assist. Since we're on the
	// system stack, this is non-preemptible, so we can
	// just measure start and end time.
	startTime := nanotime()

	decnwait := atomic.Xadd(&work.nwait, -1)
	if decnwait == work.nproc {
		println("runtime: work.nwait =", decnwait, "work.nproc=", work.nproc)
		throw("nwait > work.nprocs")
	}

	// gcDrainN requires the caller to be preemptible.
	casgstatus(gp, _Grunning, _Gwaiting)
	gp.waitreason = "GC assist marking"

	// drain own cached work first in the hopes that it
	// will be more cache friendly.
	gcw := &getg().m.p.ptr().gcw
	workDone := gcDrainN(gcw, scanWork)
	// If we are near the end of the mark phase
	// dispose of the gcw.
	if gcBlackenPromptly {
		gcw.dispose()
	}

	casgstatus(gp, _Gwaiting, _Grunning)

	// Record that we did this much scan work.
	//
	// Back out the number of bytes of assist credit that
	// this scan work counts for. The "1+" is a poor man's
	// round-up, to ensure this adds credit even if
	// assistBytesPerWork is very low.
	gp.gcAssistBytes += 1 + int64(gcController.assistBytesPerWork*float64(workDone))

	// If this is the last worker and we ran out of work,
	// signal a completion point.
	incnwait := atomic.Xadd(&work.nwait, +1)
	if incnwait > work.nproc {
		println("runtime: work.nwait=", incnwait,
			"work.nproc=", work.nproc,
			"gcBlackenPromptly=", gcBlackenPromptly)
		throw("work.nwait > work.nproc")
	}

	if incnwait == work.nproc && !gcMarkWorkAvailable(nil) {
		// This has reached a background completion point. Set
		// gp.param to a non-nil value to indicate this. It
		// doesn't matter what we set it to (it just has to be
		// a valid pointer).
		gp.param = unsafe.Pointer(gp)
	}
	duration := nanotime() - startTime
	_p_ := gp.m.p.ptr()
	_p_.gcAssistTime += duration
	if _p_.gcAssistTime > gcAssistTimeSlack {
		atomic.Xaddint64(&gcController.assistTime, _p_.gcAssistTime)
		_p_.gcAssistTime = 0
	}
}
Ejemplo n.º 17
0
// gcDrain scans roots and objects in work buffers, blackening grey
// objects until all roots and work buffers have been drained.
//
// If flags&gcDrainUntilPreempt != 0, gcDrain returns when g.preempt
// is set. This implies gcDrainNoBlock.
//
// If flags&gcDrainIdle != 0, gcDrain returns when there is other work
// to do. This implies gcDrainNoBlock.
//
// If flags&gcDrainNoBlock != 0, gcDrain returns as soon as it is
// unable to get more work. Otherwise, it will block until all
// blocking calls are blocked in gcDrain.
//
// If flags&gcDrainFlushBgCredit != 0, gcDrain flushes scan work
// credit to gcController.bgScanCredit every gcCreditSlack units of
// scan work.
//
//go:nowritebarrier
func gcDrain(gcw *gcWork, flags gcDrainFlags) {
	if !writeBarrier.needed {
		throw("gcDrain phase incorrect")
	}

	gp := getg().m.curg
	preemptible := flags&gcDrainUntilPreempt != 0
	blocking := flags&(gcDrainUntilPreempt|gcDrainIdle|gcDrainNoBlock) == 0
	flushBgCredit := flags&gcDrainFlushBgCredit != 0
	idle := flags&gcDrainIdle != 0

	initScanWork := gcw.scanWork
	// idleCheck is the scan work at which to perform the next
	// idle check with the scheduler.
	idleCheck := initScanWork + idleCheckThreshold

	// Drain root marking jobs.
	if work.markrootNext < work.markrootJobs {
		for !(preemptible && gp.preempt) {
			job := atomic.Xadd(&work.markrootNext, +1) - 1
			if job >= work.markrootJobs {
				break
			}
			markroot(gcw, job)
			if idle && pollWork() {
				goto done
			}
		}
	}

	// Drain heap marking jobs.
	for !(preemptible && gp.preempt) {
		// Try to keep work available on the global queue. We used to
		// check if there were waiting workers, but it's better to
		// just keep work available than to make workers wait. In the
		// worst case, we'll do O(log(_WorkbufSize)) unnecessary
		// balances.
		if work.full == 0 {
			gcw.balance()
		}

		var b uintptr
		if blocking {
			b = gcw.get()
		} else {
			b = gcw.tryGetFast()
			if b == 0 {
				b = gcw.tryGet()
			}
		}
		if b == 0 {
			// work barrier reached or tryGet failed.
			break
		}
		scanobject(b, gcw)

		// Flush background scan work credit to the global
		// account if we've accumulated enough locally so
		// mutator assists can draw on it.
		if gcw.scanWork >= gcCreditSlack {
			atomic.Xaddint64(&gcController.scanWork, gcw.scanWork)
			if flushBgCredit {
				gcFlushBgCredit(gcw.scanWork - initScanWork)
				initScanWork = 0
			}
			idleCheck -= gcw.scanWork
			gcw.scanWork = 0

			if idle && idleCheck <= 0 {
				idleCheck += idleCheckThreshold
				if pollWork() {
					break
				}
			}
		}
	}

	// In blocking mode, write barriers are not allowed after this
	// point because we must preserve the condition that the work
	// buffers are empty.

done:
	// Flush remaining scan work credit.
	if gcw.scanWork > 0 {
		atomic.Xaddint64(&gcController.scanWork, gcw.scanWork)
		if flushBgCredit {
			gcFlushBgCredit(gcw.scanWork - initScanWork)
		}
		gcw.scanWork = 0
	}
}
Ejemplo n.º 18
0
// push adds span s to buffer b. push is safe to call concurrently
// with other push operations, but NOT to call concurrently with pop.
func (b *gcSweepBuf) push(s *mspan) {
	// Obtain our slot.
	cursor := uintptr(atomic.Xadd(&b.index, +1) - 1)
	top, bottom := cursor/gcSweepBlockEntries, cursor%gcSweepBlockEntries

	// Do we need to add a block?
	spineLen := atomic.Loaduintptr(&b.spineLen)
	var block *gcSweepBlock
retry:
	if top < spineLen {
		spine := atomic.Loadp(unsafe.Pointer(&b.spine))
		blockp := add(spine, sys.PtrSize*top)
		block = (*gcSweepBlock)(atomic.Loadp(blockp))
	} else {
		// Add a new block to the spine, potentially growing
		// the spine.
		lock(&b.spineLock)
		// spineLen cannot change until we release the lock,
		// but may have changed while we were waiting.
		spineLen = atomic.Loaduintptr(&b.spineLen)
		if top < spineLen {
			unlock(&b.spineLock)
			goto retry
		}

		if spineLen == b.spineCap {
			// Grow the spine.
			newCap := b.spineCap * 2
			if newCap == 0 {
				newCap = gcSweepBufInitSpineCap
			}
			newSpine := persistentalloc(newCap*sys.PtrSize, sys.CacheLineSize, &memstats.gc_sys)
			if b.spineCap != 0 {
				// Blocks are allocated off-heap, so
				// no write barriers.
				memmove(newSpine, b.spine, b.spineCap*sys.PtrSize)
			}
			// Spine is allocated off-heap, so no write barrier.
			atomic.StorepNoWB(unsafe.Pointer(&b.spine), newSpine)
			b.spineCap = newCap
			// We can't immediately free the old spine
			// since a concurrent push with a lower index
			// could still be reading from it. We let it
			// leak because even a 1TB heap would waste
			// less than 2MB of memory on old spines. If
			// this is a problem, we could free old spines
			// during STW.
		}

		// Allocate a new block and add it to the spine.
		block = (*gcSweepBlock)(persistentalloc(unsafe.Sizeof(gcSweepBlock{}), sys.CacheLineSize, &memstats.gc_sys))
		blockp := add(b.spine, sys.PtrSize*top)
		// Blocks are allocated off-heap, so no write barrier.
		atomic.StorepNoWB(blockp, unsafe.Pointer(block))
		atomic.Storeuintptr(&b.spineLen, spineLen+1)
		unlock(&b.spineLock)
	}

	// We have a block. Insert the span.
	block.spans[bottom] = s
}
Ejemplo n.º 19
0
Archivo: sema.go Proyecto: 2thetop/go
// notifyListAdd adds the caller to a notify list such that it can receive
// notifications. The caller must eventually call notifyListWait to wait for
// such a notification, passing the returned ticket number.
//go:linkname notifyListAdd sync.runtime_notifyListAdd
func notifyListAdd(l *notifyList) uint32 {
	// This may be called concurrently, for example, when called from
	// sync.Cond.Wait while holding a RWMutex in read mode.
	return atomic.Xadd(&l.wait, 1) - 1
}
Ejemplo n.º 20
0
// gcDrain scans roots and objects in work buffers, blackening grey
// objects until all roots and work buffers have been drained.
//
// If flags&gcDrainUntilPreempt != 0, gcDrain returns when g.preempt
// is set. This implies gcDrainNoBlock.
//
// If flags&gcDrainNoBlock != 0, gcDrain returns as soon as it is
// unable to get more work. Otherwise, it will block until all
// blocking calls are blocked in gcDrain.
//
// If flags&gcDrainFlushBgCredit != 0, gcDrain flushes scan work
// credit to gcController.bgScanCredit every gcCreditSlack units of
// scan work.
//
//go:nowritebarrier
func gcDrain(gcw *gcWork, flags gcDrainFlags) {
	if !writeBarrier.needed {
		throw("gcDrain phase incorrect")
	}

	gp := getg()
	preemtible := flags&gcDrainUntilPreempt != 0
	blocking := flags&(gcDrainUntilPreempt|gcDrainNoBlock) == 0
	flushBgCredit := flags&gcDrainFlushBgCredit != 0

	// Drain root marking jobs.
	if work.markrootNext < work.markrootJobs {
		for blocking || !gp.preempt {
			job := atomic.Xadd(&work.markrootNext, +1) - 1
			if job >= work.markrootJobs {
				break
			}
			// TODO: Pass in gcw.
			markroot(job)
		}
	}

	initScanWork := gcw.scanWork

	// Drain heap marking jobs.
	for !(preemtible && gp.preempt) {
		// If another proc wants a pointer, give it some.
		if work.nwait > 0 && work.full == 0 {
			gcw.balance()
		}

		var b uintptr
		if blocking {
			b = gcw.get()
		} else {
			b = gcw.tryGet()
		}
		if b == 0 {
			// work barrier reached or tryGet failed.
			break
		}
		// If the current wbuf is filled by the scan a new wbuf might be
		// returned that could possibly hold only a single object. This
		// could result in each iteration draining only a single object
		// out of the wbuf passed in + a single object placed
		// into an empty wbuf in scanobject so there could be
		// a performance hit as we keep fetching fresh wbufs.
		scanobject(b, gcw)

		// Flush background scan work credit to the global
		// account if we've accumulated enough locally so
		// mutator assists can draw on it.
		if gcw.scanWork >= gcCreditSlack {
			atomic.Xaddint64(&gcController.scanWork, gcw.scanWork)
			if flushBgCredit {
				gcFlushBgCredit(gcw.scanWork - initScanWork)
				initScanWork = 0
			}
			gcw.scanWork = 0
		}
	}

	// In blocking mode, write barriers are not allowed after this
	// point because we must preserve the condition that the work
	// buffers are empty.

	// Flush remaining scan work credit.
	if gcw.scanWork > 0 {
		atomic.Xaddint64(&gcController.scanWork, gcw.scanWork)
		if flushBgCredit {
			gcFlushBgCredit(gcw.scanWork - initScanWork)
		}
		gcw.scanWork = 0
	}
}
Ejemplo n.º 21
0
Archivo: parfor.go Proyecto: hAhmadz/go
func parfordo(desc *parfor) {
	// Obtain 0-based thread index.
	tid := atomic.Xadd(&desc.thrseq, 1) - 1
	if tid >= desc.nthr {
		print("tid=", tid, " nthr=", desc.nthr, "\n")
		throw("parfor: invalid tid")
	}

	// If single-threaded, just execute the for serially.
	body := desc.body
	if desc.nthr == 1 {
		for i := uint32(0); i < desc.cnt; i++ {
			body(desc, i)
		}
		return
	}

	me := &desc.thr[tid]
	mypos := &me.pos
	for {
		for {
			// While there is local work,
			// bump low index and execute the iteration.
			pos := atomic.Xadd64(mypos, 1)
			begin := uint32(pos) - 1
			end := uint32(pos >> 32)
			if begin < end {
				body(desc, begin)
				continue
			}
			break
		}

		// Out of work, need to steal something.
		idle := false
		for try := uint32(0); ; try++ {
			// If we don't see any work for long enough,
			// increment the done counter...
			if try > desc.nthr*4 && !idle {
				idle = true
				atomic.Xadd(&desc.done, 1)
			}

			// ...if all threads have incremented the counter,
			// we are done.
			extra := uint32(0)
			if !idle {
				extra = 1
			}
			if desc.done+extra == desc.nthr {
				if !idle {
					atomic.Xadd(&desc.done, 1)
				}
				goto exit
			}

			// Choose a random victim for stealing.
			var begin, end uint32
			victim := fastrand1() % (desc.nthr - 1)
			if victim >= tid {
				victim++
			}
			victimpos := &desc.thr[victim].pos
			for {
				// See if it has any work.
				pos := atomic.Load64(victimpos)
				begin = uint32(pos)
				end = uint32(pos >> 32)
				if begin+1 >= end {
					end = 0
					begin = end
					break
				}
				if idle {
					atomic.Xadd(&desc.done, -1)
					idle = false
				}
				begin2 := begin + (end-begin)/2
				newpos := uint64(begin) | uint64(begin2)<<32
				if atomic.Cas64(victimpos, pos, newpos) {
					begin = begin2
					break
				}
			}
			if begin < end {
				// Has successfully stolen some work.
				if idle {
					throw("parfor: should not be idle")
				}
				atomic.Store64(mypos, uint64(begin)|uint64(end)<<32)
				me.nsteal++
				me.nstealcnt += uint64(end) - uint64(begin)
				break
			}

			// Backoff.
			if try < desc.nthr {
				// nothing
			} else if try < 4*desc.nthr {
				me.nprocyield++
				procyield(20)
			} else if !desc.wait {
				// If a caller asked not to wait for the others, exit now
				// (assume that most work is already done at this point).
				if !idle {
					atomic.Xadd(&desc.done, 1)
				}
				goto exit
			} else if try < 6*desc.nthr {
				me.nosyield++
				osyield()
			} else {
				me.nsleep++
				usleep(1)
			}
		}
	}

exit:
	atomic.Xadd64(&desc.nsteal, int64(me.nsteal))
	atomic.Xadd64(&desc.nstealcnt, int64(me.nstealcnt))
	atomic.Xadd64(&desc.nprocyield, int64(me.nprocyield))
	atomic.Xadd64(&desc.nosyield, int64(me.nosyield))
	atomic.Xadd64(&desc.nsleep, int64(me.nsleep))
	me.nsteal = 0
	me.nstealcnt = 0
	me.nprocyield = 0
	me.nosyield = 0
	me.nsleep = 0
}
Ejemplo n.º 22
0
// gcAssistAlloc performs GC work to make gp's assist debt positive.
// gp must be the calling user gorountine.
//
// This must be called with preemption enabled.
//go:nowritebarrier
func gcAssistAlloc(gp *g) {
	// Don't assist in non-preemptible contexts. These are
	// generally fragile and won't allow the assist to block.
	if getg() == gp.m.g0 {
		return
	}
	if mp := getg().m; mp.locks > 0 || mp.preemptoff != "" {
		return
	}

	// Compute the amount of scan work we need to do to make the
	// balance positive. We over-assist to build up credit for
	// future allocations and amortize the cost of assisting.
	debtBytes := -gp.gcAssistBytes + gcOverAssistBytes
	scanWork := int64(gcController.assistWorkPerByte * float64(debtBytes))

retry:
	// Steal as much credit as we can from the background GC's
	// scan credit. This is racy and may drop the background
	// credit below 0 if two mutators steal at the same time. This
	// will just cause steals to fail until credit is accumulated
	// again, so in the long run it doesn't really matter, but we
	// do have to handle the negative credit case.
	bgScanCredit := atomic.Loadint64(&gcController.bgScanCredit)
	stolen := int64(0)
	if bgScanCredit > 0 {
		if bgScanCredit < scanWork {
			stolen = bgScanCredit
			gp.gcAssistBytes += 1 + int64(gcController.assistBytesPerWork*float64(stolen))
		} else {
			stolen = scanWork
			gp.gcAssistBytes += debtBytes
		}
		atomic.Xaddint64(&gcController.bgScanCredit, -stolen)

		scanWork -= stolen

		if scanWork == 0 {
			// We were able to steal all of the credit we
			// needed.
			return
		}
	}

	// Perform assist work
	completed := false
	systemstack(func() {
		if atomic.Load(&gcBlackenEnabled) == 0 {
			// The gcBlackenEnabled check in malloc races with the
			// store that clears it but an atomic check in every malloc
			// would be a performance hit.
			// Instead we recheck it here on the non-preemptable system
			// stack to determine if we should preform an assist.

			// GC is done, so ignore any remaining debt.
			gp.gcAssistBytes = 0
			return
		}
		// Track time spent in this assist. Since we're on the
		// system stack, this is non-preemptible, so we can
		// just measure start and end time.
		startTime := nanotime()

		decnwait := atomic.Xadd(&work.nwait, -1)
		if decnwait == work.nproc {
			println("runtime: work.nwait =", decnwait, "work.nproc=", work.nproc)
			throw("nwait > work.nprocs")
		}

		// drain own cached work first in the hopes that it
		// will be more cache friendly.
		gcw := &getg().m.p.ptr().gcw
		workDone := gcDrainN(gcw, scanWork)
		// If we are near the end of the mark phase
		// dispose of the gcw.
		if gcBlackenPromptly {
			gcw.dispose()
		}

		// Record that we did this much scan work.
		//
		// Back out the number of bytes of assist credit that
		// this scan work counts for. The "1+" is a poor man's
		// round-up, to ensure this adds credit even if
		// assistBytesPerWork is very low.
		gp.gcAssistBytes += 1 + int64(gcController.assistBytesPerWork*float64(workDone))

		// If this is the last worker and we ran out of work,
		// signal a completion point.
		incnwait := atomic.Xadd(&work.nwait, +1)
		if incnwait > work.nproc {
			println("runtime: work.nwait=", incnwait,
				"work.nproc=", work.nproc,
				"gcBlackenPromptly=", gcBlackenPromptly)
			throw("work.nwait > work.nproc")
		}

		if incnwait == work.nproc && !gcMarkWorkAvailable(nil) {
			// This has reached a background completion
			// point.
			completed = true
		}
		duration := nanotime() - startTime
		_p_ := gp.m.p.ptr()
		_p_.gcAssistTime += duration
		if _p_.gcAssistTime > gcAssistTimeSlack {
			atomic.Xaddint64(&gcController.assistTime, _p_.gcAssistTime)
			_p_.gcAssistTime = 0
		}
	})

	if completed {
		gcMarkDone()
	}

	if gp.gcAssistBytes < 0 {
		// We were unable steal enough credit or perform
		// enough work to pay off the assist debt. We need to
		// do one of these before letting the mutator allocate
		// more to prevent over-allocation.
		//
		// If this is because we were preempted, reschedule
		// and try some more.
		if gp.preempt {
			Gosched()
			goto retry
		}

		// Add this G to an assist queue and park. When the GC
		// has more background credit, it will satisfy queued
		// assists before flushing to the global credit pool.
		//
		// Note that this does *not* get woken up when more
		// work is added to the work list. The theory is that
		// there wasn't enough work to do anyway, so we might
		// as well let background marking take care of the
		// work that is available.
		lock(&work.assistQueue.lock)

		// If the GC cycle is over, just return. This is the
		// likely path if we completed above. We do this
		// under the lock to prevent a GC cycle from ending
		// between this check and queuing the assist.
		if atomic.Load(&gcBlackenEnabled) == 0 {
			unlock(&work.assistQueue.lock)
			return
		}

		oldHead, oldTail := work.assistQueue.head, work.assistQueue.tail
		if oldHead == 0 {
			work.assistQueue.head.set(gp)
		} else {
			oldTail.ptr().schedlink.set(gp)
		}
		work.assistQueue.tail.set(gp)
		gp.schedlink.set(nil)
		// Recheck for background credit now that this G is in
		// the queue, but can still back out. This avoids a
		// race in case background marking has flushed more
		// credit since we checked above.
		if atomic.Loadint64(&gcController.bgScanCredit) > 0 {
			work.assistQueue.head = oldHead
			work.assistQueue.tail = oldTail
			if oldTail != 0 {
				oldTail.ptr().schedlink.set(nil)
			}
			unlock(&work.assistQueue.lock)
			goto retry
		}
		// Park for real.
		goparkunlock(&work.assistQueue.lock, "GC assist wait", traceEvGoBlock, 2)

		// At this point either background GC has satisfied
		// this G's assist debt, or the GC cycle is over.
	}
}