src/cmd/compile/internal/base/base.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package base

 import (
 	"fmt"
 	"os"
 	"runtime"
 	"runtime/debug"
 	"runtime/metrics"
 )

 var atExitFuncs []func()

 func AtExit(f func()) {
 	atExitFuncs = append(atExitFuncs, f)
 }

 func Exit(code int) {
 	for i := len(atExitFuncs) - 1; i >= 0; i-- {
 		f := atExitFuncs[i]
 		atExitFuncs = atExitFuncs[:i]
 		f()
 	}
 	os.Exit(code)
 }

 // To enable tracing support (-t flag), set EnableTrace to true.
 const EnableTrace = false

 // forEachGC calls fn each GC cycle until it returns false.
 func forEachGC(fn func() bool) {
 	type T [32]byte // large enough to avoid runtime's tiny object allocator

 	var finalizer func(*T)
 	finalizer = func(p *T) {
 		if fn() {
 			runtime.SetFinalizer(p, finalizer)
 		}
 	}

 	finalizer(new(T))
 }

 // AdjustStartingHeap modifies GOGC so that GC should not occur until the heap
 // grows to the requested size.  This is intended but not promised, though it
 // is true-mostly, depending on when the adjustment occurs and on the
 // compiler's input and behavior.  Once this size is approximately reached
 // GOGC is reset to 100; subsequent GCs may reduce the heap below the requested
 // size, but this function does not affect that.
 //
 // -d=gcadjust=1 enables logging of GOGC adjustment events.
 //
 // NOTE: If you think this code would help startup time in your own
 // application and you decide to use it, please benchmark first to see if it
 // actually works for you (it may not: the Go compiler is not typical), and
 // whatever the outcome, please leave a comment on bug #56546.  This code
 // uses supported interfaces, but depends more than we like on
 // current+observed behavior of the garbage collector, so if many people need
 // this feature, we should consider/propose a better way to accomplish it.
 func AdjustStartingHeap(requestedHeapGoal uint64) {
 	logHeapTweaks := Debug.GCAdjust == 1
 	mp := runtime.GOMAXPROCS(0)
 	gcConcurrency := Flag.LowerC

 	const (
 		goal   = "/gc/heap/goal:bytes"
 		count  = "/gc/cycles/total:gc-cycles"
 		allocs = "/gc/heap/allocs:bytes"
 		frees  = "/gc/heap/frees:bytes"
 	)

 	sample := []metrics.Sample{{Name: goal}, {Name: count}, {Name: allocs}, {Name: frees}}
 	const (
 		GOAL   = 0
 		COUNT  = 1
 		ALLOCS = 2
 		FREES  = 3
 	)

 	// Assumptions and observations of Go's garbage collector, as of Go 1.17-1.20:

 	// - the initial heap goal is 4M, by fiat.  It is possible for Go to start
 	//   with a heap as small as 512k, so this may change in the future.

 	// - except for the first heap goal, heap goal is a function of
 	//   observed-live at the previous GC and current GOGC.  After the first
 	//   GC, adjusting GOGC immediately updates GOGC; before the first GC,
 	//   adjusting GOGC does not modify goal (but the change takes effect after
 	//   the first GC).

 	// - the before/after first GC behavior is not guaranteed anywhere, it's
 	//   just behavior, and it's a bad idea to rely on it.

 	// - we don't know exactly when GC will run, even after we adjust GOGC; the
 	//   first GC may not have happened yet, may have already happened, or may
 	//   be currently in progress, and GCs can start for several reasons.

 	// - forEachGC above will run the provided function at some delay after each
 	//   GC's mark phase terminates; finalizers are run after marking as the
 	//   spans containing finalizable objects are swept, driven by GC
 	//   background activity and allocation demand.

 	// - "live at last GC" is not available through the current metrics
 	//    interface. Instead, live is estimated by knowing the adjusted value of
 	//    GOGC and the new heap goal following a GC (this requires knowing that
 	//    at least one GC has occurred):
 	//		  estLive = 100 * newGoal / (100 + currentGogc)]
 	//    this new value of GOGC
 	//		  newGogc = 100*requestedHeapGoal/estLive - 100
 	//    will result in the desired goal. The logging code checks that the
 	//    resulting goal is correct.

 	// There's a small risk that the finalizer will be slow to run after a GC
 	// that expands the goal to a huge value, and that this will lead to
 	// out-of-memory.  This doesn't seem to happen; in experiments on a variety
 	// of machines with a variety of extra loads to disrupt scheduling, the
 	// worst overshoot observed was 50% past requestedHeapGoal.

 	metrics.Read(sample)
 	for _, s := range sample {
 		if s.Value.Kind() == metrics.KindBad {
 			// Just return, a slightly slower compilation is a tolerable outcome.
 			if logHeapTweaks {
 				fmt.Fprintf(os.Stderr, "GCAdjust: Regret unexpected KindBad for metric %s\n", s.Name)
 			}
 			return
 		}
 	}

 	// Tinker with GOGC to make the heap grow rapidly at first.
 	currentGoal := sample[GOAL].Value.Uint64() // Believe this will be 4MByte or less, perhaps 512k
 	myGogc := 100 * requestedHeapGoal / currentGoal
 	if myGogc <= 150 {
 		return
 	}

 	if logHeapTweaks {
 		sample := append([]metrics.Sample(nil), sample...) // avoid races with GC callback
 		AtExit(func() {
 			metrics.Read(sample)
 			goal := sample[GOAL].Value.Uint64()
 			count := sample[COUNT].Value.Uint64()
 			oldGogc := debug.SetGCPercent(100)
 			if oldGogc == 100 {
 				fmt.Fprintf(os.Stderr, "GCAdjust: AtExit goal %d gogc %d count %d maxprocs %d gcConcurrency %d\n",
 					goal, oldGogc, count, mp, gcConcurrency)
 			} else {
 				inUse := sample[ALLOCS].Value.Uint64() - sample[FREES].Value.Uint64()
 				overPct := 100 * (int(inUse) - int(requestedHeapGoal)) / int(requestedHeapGoal)
 				fmt.Fprintf(os.Stderr, "GCAdjust: AtExit goal %d gogc %d count %d maxprocs %d gcConcurrency %d overPct %d\n",
 					goal, oldGogc, count, mp, gcConcurrency, overPct)

 			}
 		})
 	}

 	debug.SetGCPercent(int(myGogc))

 	adjustFunc := func() bool {

 		metrics.Read(sample)
 		goal := sample[GOAL].Value.Uint64()
 		count := sample[COUNT].Value.Uint64()

 		if goal <= requestedHeapGoal { // Stay the course
 			if logHeapTweaks {
 				fmt.Fprintf(os.Stderr, "GCAdjust: Reuse GOGC adjust, current goal %d, count is %d, current gogc %d\n",
 					goal, count, myGogc)
 			}
 			return true
 		}

 		// Believe goal has been adjusted upwards, else it would be less-than-or-equal than requestedHeapGoal
 		calcLive := 100 * goal / (100 + myGogc)

 		if 2*calcLive < requestedHeapGoal { // calcLive can exceed requestedHeapGoal!
 			myGogc = 100*requestedHeapGoal/calcLive - 100

 			if myGogc > 125 {
 				// Not done growing the heap.
 				oldGogc := debug.SetGCPercent(int(myGogc))

 				if logHeapTweaks {
 					// Check that the new goal looks right
 					inUse := sample[ALLOCS].Value.Uint64() - sample[FREES].Value.Uint64()
 					metrics.Read(sample)
 					newGoal := sample[GOAL].Value.Uint64()
 					pctOff := 100 * (int64(newGoal) - int64(requestedHeapGoal)) / int64(requestedHeapGoal)
 					// Check that the new goal is close to requested.  3% of make.bash fails this test.  Why, TBD.
 					if pctOff < 2 {
 						fmt.Fprintf(os.Stderr, "GCAdjust: Retry GOGC adjust, current goal %d, count is %d, gogc was %d, is now %d, calcLive %d pctOff %d\n",
 							goal, count, oldGogc, myGogc, calcLive, pctOff)
 					} else {
 						// The GC is being annoying and not giving us the goal that we requested, say more to help understand when/why.
 						fmt.Fprintf(os.Stderr, "GCAdjust: Retry GOGC adjust, current goal %d, count is %d, gogc was %d, is now %d, calcLive %d pctOff %d inUse %d\n",
 							goal, count, oldGogc, myGogc, calcLive, pctOff, inUse)
 					}
 				}
 				return true
 			}
 		}

 		// In this case we're done boosting GOGC, set it to 100 and don't set a new finalizer.
 		oldGogc := debug.SetGCPercent(100)
 		// inUse helps estimate how late the finalizer ran; at the instant the previous GC ended,
 		// it was (in theory) equal to the previous GC's heap goal.  In a growing heap it is
 		// expected to grow to the new heap goal.
 		inUse := sample[ALLOCS].Value.Uint64() - sample[FREES].Value.Uint64()
 		overPct := 100 * (int(inUse) - int(requestedHeapGoal)) / int(requestedHeapGoal)
 		if logHeapTweaks {
 			fmt.Fprintf(os.Stderr, "GCAdjust: Reset GOGC adjust, old goal %d, count is %d, gogc was %d, calcLive %d inUse %d overPct %d\n",
 				goal, count, oldGogc, calcLive, inUse, overPct)
 		}
 		return false
 	}

 	forEachGC(adjustFunc)
 }

 func Compiling(pkgs []string) bool {
 	if Ctxt.Pkgpath != "" {
 		for _, p := range pkgs {
 			if Ctxt.Pkgpath == p {
 				return true
 			}
 		}
 	}

 	return false
 }

 // The racewalk pass is currently handled in three parts.
 //
 // First, for flag_race, it inserts calls to racefuncenter and
 // racefuncexit at the start and end (respectively) of each
 // function. This is handled below.
 //
 // Second, during buildssa, it inserts appropriate instrumentation
 // calls immediately before each memory load or store. This is handled
 // by the (*state).instrument method in ssa.go, so here we just set
 // the Func.InstrumentBody flag as needed. For background on why this
 // is done during SSA construction rather than a separate SSA pass,
 // see issue #19054.
 //
 // Third we remove calls to racefuncenter and racefuncexit, for leaf
 // functions without instrumented operations. This is done as part of
 // ssa opt pass via special rule.

 // TODO(dvyukov): do not instrument initialization as writes:
 // a := make([]int, 10)

 // Do not instrument the following packages at all,
 // at best instrumentation would cause infinite recursion.
 var NoInstrumentPkgs = []string{
 	"runtime/internal/atomic",
 	"runtime/internal/math",
 	"runtime/internal/sys",
 	"runtime/internal/syscall",
 	"runtime",
 	"runtime/race",
 	"runtime/msan",
 	"runtime/asan",
 	"internal/cpu",
 }

 // Don't insert racefuncenter/racefuncexit into the following packages.
 // Memory accesses in the packages are either uninteresting or will cause false positives.
 var NoRacePkgs = []string{"sync", "sync/atomic"}
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package base

	import (
	"fmt"
	"os"
	"runtime"
	"runtime/debug"
	"runtime/metrics"
	)

	var atExitFuncs []func()

	func AtExit(f func()) {
	atExitFuncs = append(atExitFuncs, f)
	}

	func Exit(code int) {
	for i := len(atExitFuncs) - 1; i >= 0; i-- {
	f := atExitFuncs[i]
	atExitFuncs = atExitFuncs[:i]
	f()
	}
	os.Exit(code)
	}

	// To enable tracing support (-t flag), set EnableTrace to true.
	const EnableTrace = false

	// forEachGC calls fn each GC cycle until it returns false.
	func forEachGC(fn func() bool) {
	type T [32]byte // large enough to avoid runtime's tiny object allocator

	var finalizer func(*T)
	finalizer = func(p *T) {
	if fn() {
	runtime.SetFinalizer(p, finalizer)
	}
	}

	finalizer(new(T))
	}

	// AdjustStartingHeap modifies GOGC so that GC should not occur until the heap
	// grows to the requested size. This is intended but not promised, though it
	// is true-mostly, depending on when the adjustment occurs and on the
	// compiler's input and behavior. Once this size is approximately reached
	// GOGC is reset to 100; subsequent GCs may reduce the heap below the requested
	// size, but this function does not affect that.
	//
	// -d=gcadjust=1 enables logging of GOGC adjustment events.
	//
	// NOTE: If you think this code would help startup time in your own
	// application and you decide to use it, please benchmark first to see if it
	// actually works for you (it may not: the Go compiler is not typical), and
	// whatever the outcome, please leave a comment on bug #56546. This code
	// uses supported interfaces, but depends more than we like on
	// current+observed behavior of the garbage collector, so if many people need
	// this feature, we should consider/propose a better way to accomplish it.
	func AdjustStartingHeap(requestedHeapGoal uint64) {
	logHeapTweaks := Debug.GCAdjust == 1
	mp := runtime.GOMAXPROCS(0)
	gcConcurrency := Flag.LowerC

	const (
	goal = "/gc/heap/goal:bytes"
	count = "/gc/cycles/total:gc-cycles"
	allocs = "/gc/heap/allocs:bytes"
	frees = "/gc/heap/frees:bytes"
	)

	sample := []metrics.Sample{{Name: goal}, {Name: count}, {Name: allocs}, {Name: frees}}
	const (
	GOAL = 0
	COUNT = 1
	ALLOCS = 2
	FREES = 3
	)

	// Assumptions and observations of Go's garbage collector, as of Go 1.17-1.20:

	// - the initial heap goal is 4M, by fiat. It is possible for Go to start
	// with a heap as small as 512k, so this may change in the future.

	// - except for the first heap goal, heap goal is a function of
	// observed-live at the previous GC and current GOGC. After the first
	// GC, adjusting GOGC immediately updates GOGC; before the first GC,
	// adjusting GOGC does not modify goal (but the change takes effect after
	// the first GC).

	// - the before/after first GC behavior is not guaranteed anywhere, it's
	// just behavior, and it's a bad idea to rely on it.

	// - we don't know exactly when GC will run, even after we adjust GOGC; the
	// first GC may not have happened yet, may have already happened, or may
	// be currently in progress, and GCs can start for several reasons.

	// - forEachGC above will run the provided function at some delay after each
	// GC's mark phase terminates; finalizers are run after marking as the
	// spans containing finalizable objects are swept, driven by GC
	// background activity and allocation demand.

	// - "live at last GC" is not available through the current metrics
	// interface. Instead, live is estimated by knowing the adjusted value of
	// GOGC and the new heap goal following a GC (this requires knowing that
	// at least one GC has occurred):
	// estLive = 100 * newGoal / (100 + currentGogc)]
	// this new value of GOGC
	// newGogc = 100*requestedHeapGoal/estLive - 100
	// will result in the desired goal. The logging code checks that the
	// resulting goal is correct.

	// There's a small risk that the finalizer will be slow to run after a GC
	// that expands the goal to a huge value, and that this will lead to
	// out-of-memory. This doesn't seem to happen; in experiments on a variety
	// of machines with a variety of extra loads to disrupt scheduling, the
	// worst overshoot observed was 50% past requestedHeapGoal.

	metrics.Read(sample)
	for _, s := range sample {
	if s.Value.Kind() == metrics.KindBad {
	// Just return, a slightly slower compilation is a tolerable outcome.
	if logHeapTweaks {
	fmt.Fprintf(os.Stderr, "GCAdjust: Regret unexpected KindBad for metric %s\n", s.Name)
	}
	return
	}
	}

	// Tinker with GOGC to make the heap grow rapidly at first.
	currentGoal := sample[GOAL].Value.Uint64() // Believe this will be 4MByte or less, perhaps 512k
	myGogc := 100 * requestedHeapGoal / currentGoal
	if myGogc <= 150 {
	return
	}

	if logHeapTweaks {
	sample := append([]metrics.Sample(nil), sample...) // avoid races with GC callback
	AtExit(func() {
	metrics.Read(sample)
	goal := sample[GOAL].Value.Uint64()
	count := sample[COUNT].Value.Uint64()
	oldGogc := debug.SetGCPercent(100)
	if oldGogc == 100 {
	fmt.Fprintf(os.Stderr, "GCAdjust: AtExit goal %d gogc %d count %d maxprocs %d gcConcurrency %d\n",
	goal, oldGogc, count, mp, gcConcurrency)
	} else {
	inUse := sample[ALLOCS].Value.Uint64() - sample[FREES].Value.Uint64()
	overPct := 100 * (int(inUse) - int(requestedHeapGoal)) / int(requestedHeapGoal)
	fmt.Fprintf(os.Stderr, "GCAdjust: AtExit goal %d gogc %d count %d maxprocs %d gcConcurrency %d overPct %d\n",
	goal, oldGogc, count, mp, gcConcurrency, overPct)

	}
	})
	}

	debug.SetGCPercent(int(myGogc))

	adjustFunc := func() bool {

	metrics.Read(sample)
	goal := sample[GOAL].Value.Uint64()
	count := sample[COUNT].Value.Uint64()

	if goal <= requestedHeapGoal { // Stay the course
	if logHeapTweaks {
	fmt.Fprintf(os.Stderr, "GCAdjust: Reuse GOGC adjust, current goal %d, count is %d, current gogc %d\n",
	goal, count, myGogc)
	}
	return true
	}

	// Believe goal has been adjusted upwards, else it would be less-than-or-equal than requestedHeapGoal
	calcLive := 100 * goal / (100 + myGogc)

	if 2*calcLive < requestedHeapGoal { // calcLive can exceed requestedHeapGoal!
	myGogc = 100*requestedHeapGoal/calcLive - 100

	if myGogc > 125 {
	// Not done growing the heap.
	oldGogc := debug.SetGCPercent(int(myGogc))

	if logHeapTweaks {
	// Check that the new goal looks right
	inUse := sample[ALLOCS].Value.Uint64() - sample[FREES].Value.Uint64()
	metrics.Read(sample)
	newGoal := sample[GOAL].Value.Uint64()
	pctOff := 100 * (int64(newGoal) - int64(requestedHeapGoal)) / int64(requestedHeapGoal)
	// Check that the new goal is close to requested. 3% of make.bash fails this test. Why, TBD.
	if pctOff < 2 {
	fmt.Fprintf(os.Stderr, "GCAdjust: Retry GOGC adjust, current goal %d, count is %d, gogc was %d, is now %d, calcLive %d pctOff %d\n",
	goal, count, oldGogc, myGogc, calcLive, pctOff)
	} else {
	// The GC is being annoying and not giving us the goal that we requested, say more to help understand when/why.
	fmt.Fprintf(os.Stderr, "GCAdjust: Retry GOGC adjust, current goal %d, count is %d, gogc was %d, is now %d, calcLive %d pctOff %d inUse %d\n",
	goal, count, oldGogc, myGogc, calcLive, pctOff, inUse)
	}
	}
	return true
	}
	}

	// In this case we're done boosting GOGC, set it to 100 and don't set a new finalizer.
	oldGogc := debug.SetGCPercent(100)
	// inUse helps estimate how late the finalizer ran; at the instant the previous GC ended,
	// it was (in theory) equal to the previous GC's heap goal. In a growing heap it is
	// expected to grow to the new heap goal.
	inUse := sample[ALLOCS].Value.Uint64() - sample[FREES].Value.Uint64()
	overPct := 100 * (int(inUse) - int(requestedHeapGoal)) / int(requestedHeapGoal)
	if logHeapTweaks {
	fmt.Fprintf(os.Stderr, "GCAdjust: Reset GOGC adjust, old goal %d, count is %d, gogc was %d, calcLive %d inUse %d overPct %d\n",
	goal, count, oldGogc, calcLive, inUse, overPct)
	}
	return false
	}

	forEachGC(adjustFunc)
	}

	func Compiling(pkgs []string) bool {
	if Ctxt.Pkgpath != "" {
	for _, p := range pkgs {
	if Ctxt.Pkgpath == p {
	return true
	}
	}
	}

	return false
	}

	// The racewalk pass is currently handled in three parts.
	//
	// First, for flag_race, it inserts calls to racefuncenter and
	// racefuncexit at the start and end (respectively) of each
	// function. This is handled below.
	//
	// Second, during buildssa, it inserts appropriate instrumentation
	// calls immediately before each memory load or store. This is handled
	// by the (*state).instrument method in ssa.go, so here we just set
	// the Func.InstrumentBody flag as needed. For background on why this
	// is done during SSA construction rather than a separate SSA pass,
	// see issue #19054.
	//
	// Third we remove calls to racefuncenter and racefuncexit, for leaf
	// functions without instrumented operations. This is done as part of
	// ssa opt pass via special rule.

	// TODO(dvyukov): do not instrument initialization as writes:
	// a := make([]int, 10)

	// Do not instrument the following packages at all,
	// at best instrumentation would cause infinite recursion.
	var NoInstrumentPkgs = []string{
	"runtime/internal/atomic",
	"runtime/internal/math",
	"runtime/internal/sys",
	"runtime/internal/syscall",
	"runtime",
	"runtime/race",
	"runtime/msan",
	"runtime/asan",
	"internal/cpu",
	}

	// Don't insert racefuncenter/racefuncexit into the following packages.
	// Memory accesses in the packages are either uninteresting or will cause false positives.
	var NoRacePkgs = []string{"sync", "sync/atomic"}