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Revert "sync: improve sync.Pool object stealing"
This reverts CL 303949. Reason for revert: broke linux-arm-aws TryBots. Change-Id: Ib44949df70520cdabff857846be0d2221403d2f4 Reviewed-on: https://go-review.googlesource.com/c/go/+/313630 Trust: Bryan C. Mills <bcmills@google.com> Run-TryBot: Bryan C. Mills <bcmills@google.com> Reviewed-by: Cherry Zhang <cherryyz@google.com> TryBot-Result: Go Bot <gobot@golang.org>
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c430313992
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0d1280c685
103
src/sync/pool.go
103
src/sync/pool.go
@ -70,57 +70,6 @@ type poolLocal struct {
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pad [128 - unsafe.Sizeof(poolLocalInternal{})%128]byte
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}
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// The randomOrder and randomEnum are copied from runtime/proc.go
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type randomOrder struct {
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count uint32
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coprimes []uint32
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}
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type randomEnum struct {
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i uint32
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count uint32
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pos uint32
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inc uint32
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}
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func (ord *randomOrder) reset(count uint32) {
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ord.count = count
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ord.coprimes = ord.coprimes[:0]
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for i := uint32(1); i <= count; i++ {
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if gcd(i, count) == 1 {
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ord.coprimes = append(ord.coprimes, i)
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}
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}
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}
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func (ord *randomOrder) start(i uint32) randomEnum {
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return randomEnum{
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count: ord.count,
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pos: i % ord.count,
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inc: ord.coprimes[i%uint32(len(ord.coprimes))],
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}
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}
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func (enum *randomEnum) done() bool {
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return enum.i == enum.count
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}
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func (enum *randomEnum) next() {
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enum.i++
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enum.pos = (enum.pos + enum.inc) % enum.count
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}
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func (enum *randomEnum) position() uint32 {
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return enum.pos
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}
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func gcd(a, b uint32) uint32 {
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for b != 0 {
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a, b = b, a%b
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}
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return a
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}
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// from runtime
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func fastrand() uint32
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@ -204,27 +153,12 @@ func (p *Pool) Get() interface{} {
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func (p *Pool) getSlow(pid int) interface{} {
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// See the comment in pin regarding ordering of the loads.
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size := runtime_LoadAcquintptr(&p.localSize) // load-acquire
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// Load pOrder atomically to prevent possible races
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order := (*randomOrder)(atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&pOrder)))) // load-consume
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// Pin function always returns non-zero localSize, and it will remain so until runtime_procUnpin
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// is called. This invariant is maintained by pin ensuring that locals is always big enough to
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// account for the current P and that poolCleanup can never execute concurrently with a pinned P
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// due to disabled preemtion.
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// So, we can remove this condition which protects from division by zero in loop's body,
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// but we leave it here just to be sure there is no any possibility for error
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if size != 0 {
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locals := p.local // load-consume
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// Try to steal one element from other procs.
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for rndp := order.start(fastrand()); !rndp.done(); rndp.next() {
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i := int(rndp.position())
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// While pOrder is limited to returning indexes within the range of Ps,
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// locals may be smaller either because it was reset or because of a race
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// with pinSlow. Hence, we must still mod the local index by size.
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l := indexLocal(locals, (pid+i+1)%int(size))
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if x, _ := l.shared.popTail(); x != nil {
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return x
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}
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locals := p.local // load-consume
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// Try to steal one element from other procs.
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for i := 0; i < int(size); i++ {
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l := indexLocal(locals, (pid+i+1)%int(size))
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if x, _ := l.shared.popTail(); x != nil {
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return x
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}
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}
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@ -232,25 +166,16 @@ func (p *Pool) getSlow(pid int) interface{} {
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// from all primary caches because we want objects in the
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// victim cache to age out if at all possible.
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size = atomic.LoadUintptr(&p.victimSize)
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// We also have to ensure that victim cache is big enough to account current P
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// and size is not equal to zero (protects from division by zero) similar as pin
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// function do
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if uintptr(pid) >= size {
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return nil
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}
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locals := p.victim
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locals = p.victim
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l := indexLocal(locals, pid)
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// Check private cache
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if x := l.private; x != nil {
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l.private = nil
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return x
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}
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// Try to fetch from the tail of other P queues
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for rndp := order.start(fastrand()); !rndp.done(); rndp.next() {
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i := int(rndp.position())
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for i := 0; i < int(size); i++ {
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l := indexLocal(locals, (pid+i)%int(size))
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if x, _ := l.shared.popTail(); x != nil {
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return x
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@ -299,13 +224,9 @@ func (p *Pool) pinSlow() (*poolLocal, int) {
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}
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// If GOMAXPROCS changes between GCs, we re-allocate the array and lose the old one.
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size := runtime.GOMAXPROCS(0)
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// Set count of Ps for random ordering
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order := &randomOrder{}
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order.reset(uint32(size))
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local := make([]poolLocal, size)
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atomic.StorePointer(&p.local, unsafe.Pointer(&local[0])) // store-release
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atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&pOrder)), unsafe.Pointer(order)) // store-release
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runtime_StoreReluintptr(&p.localSize, uintptr(size)) // store-release
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atomic.StorePointer(&p.local, unsafe.Pointer(&local[0])) // store-release
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runtime_StoreReluintptr(&p.localSize, uintptr(size)) // store-release
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return &local[pid], pid
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}
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@ -346,10 +267,6 @@ var (
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// oldPools is the set of pools that may have non-empty victim
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// caches. Protected by STW.
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oldPools []*Pool
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// pOrder is a random order of Ps used for stealing. Writes
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// are protected by allPoolsMu. Reads are atomic.
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pOrder *randomOrder
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)
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func init() {
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@ -271,24 +271,6 @@ func BenchmarkPoolOverflow(b *testing.B) {
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})
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}
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// Simulate object starvation in order to force Ps to steal objects
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// from other Ps.
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func BenchmarkPoolStarvation(b *testing.B) {
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var p Pool
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count := 100
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count_starved := count - (count / runtime.GOMAXPROCS(0))
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b.RunParallel(func(pb *testing.PB) {
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for pb.Next() {
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for b := 0; b < count_starved; b++ {
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p.Put(1)
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}
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for b := 0; b < count; b++ {
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p.Get()
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}
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}
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})
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}
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var globalSink interface{}
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func BenchmarkPoolSTW(b *testing.B) {
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