From b65c93b2b465e1c96ffd6a4554996acccf468ce1 Mon Sep 17 00:00:00 2001 From: Jakub Sztandera Date: Fri, 19 May 2023 19:43:56 +0200 Subject: [PATCH] feat: chainstore: sharded mutex for filling chain height index This PR introduces as sharded mutex within the ChainIndex#GetTipsetByHeight. It also replaces a go map with xsync.Map which doesn't require locking. The lock is taken when it appears that ChainIndex filling work should be started. After claiming the lock, the status of the cache is rechecked, if the entry is still missing, the fillCache is started. Thanks to @snissn and @arajasek for debugging and taking initial stabs at this. Supersedes #10866 and 10885 Signed-off-by: Jakub Sztandera --- chain/store/index.go | 44 ++++--- go.mod | 1 + go.sum | 2 + lib/shardedmutex/shardedmutex.go | 75 ++++++++++++ lib/shardedmutex/shardedmutex_test.go | 159 ++++++++++++++++++++++++++ 5 files changed, 266 insertions(+), 15 deletions(-) create mode 100644 lib/shardedmutex/shardedmutex.go create mode 100644 lib/shardedmutex/shardedmutex_test.go diff --git a/chain/store/index.go b/chain/store/index.go index 620cb2dee..5807a2705 100644 --- a/chain/store/index.go +++ b/chain/store/index.go @@ -2,18 +2,21 @@ package store import ( "context" + "hash/maphash" "os" "strconv" - "sync" + "github.com/puzpuzpuz/xsync/v2" "golang.org/x/xerrors" "github.com/filecoin-project/go-state-types/abi" "github.com/filecoin-project/lotus/chain/types" + "github.com/filecoin-project/lotus/lib/shardedmutex" ) -var DefaultChainIndexCacheSize = 32 << 15 +// DefaultChainIndexCacheSize no longer sets the maximum size, just the inital size of the map. +var DefaultChainIndexCacheSize = 1 << 15 func init() { if s := os.Getenv("LOTUS_CHAIN_INDEX_CACHE"); s != "" { @@ -27,8 +30,9 @@ func init() { } type ChainIndex struct { - indexCacheLk sync.Mutex - indexCache map[types.TipSetKey]*lbEntry + indexCache *xsync.MapOf[types.TipSetKey, *lbEntry] + + fillCacheLock shardedmutex.ShardedMutexFor[types.TipSetKey] loadTipSet loadTipSetFunc @@ -36,11 +40,16 @@ type ChainIndex struct { } type loadTipSetFunc func(context.Context, types.TipSetKey) (*types.TipSet, error) +func maphashTSK(s maphash.Seed, tsk types.TipSetKey) uint64 { + return maphash.Bytes(s, tsk.Bytes()) +} + func NewChainIndex(lts loadTipSetFunc) *ChainIndex { return &ChainIndex{ - indexCache: make(map[types.TipSetKey]*lbEntry, DefaultChainIndexCacheSize), - loadTipSet: lts, - skipLength: 20, + indexCache: xsync.NewTypedMapOfPresized[types.TipSetKey, *lbEntry](maphashTSK, DefaultChainIndexCacheSize), + fillCacheLock: shardedmutex.NewFor(maphashTSK, 32), + loadTipSet: lts, + skipLength: 20, } } @@ -59,17 +68,23 @@ func (ci *ChainIndex) GetTipsetByHeight(ctx context.Context, from *types.TipSet, return nil, xerrors.Errorf("failed to round down: %w", err) } - ci.indexCacheLk.Lock() - defer ci.indexCacheLk.Unlock() cur := rounded.Key() for { - lbe, ok := ci.indexCache[cur] + lbe, ok := ci.indexCache.Load(cur) // check the cache if !ok { - fc, err := ci.fillCache(ctx, cur) - if err != nil { - return nil, xerrors.Errorf("failed to fill cache: %w", err) + lk := ci.fillCacheLock.GetLock(cur) + lk.Lock() // if entry is missing, take the lock + lbe, ok = ci.indexCache.Load(cur) // check if someone else added it while we waited for lock + if !ok { + fc, err := ci.fillCache(ctx, cur) + if err != nil { + lk.Unlock() + return nil, xerrors.Errorf("failed to fill cache: %w", err) + } + lbe = fc + ci.indexCache.Store(cur, lbe) } - lbe = fc + lk.Unlock() } if to == lbe.targetHeight { @@ -137,7 +152,6 @@ func (ci *ChainIndex) fillCache(ctx context.Context, tsk types.TipSetKey) (*lbEn targetHeight: skipTarget.Height(), target: skipTarget.Key(), } - ci.indexCache[tsk] = lbe return lbe, nil } diff --git a/go.mod b/go.mod index d190323f2..f19c6d3ca 100644 --- a/go.mod +++ b/go.mod @@ -139,6 +139,7 @@ require ( github.com/open-rpc/meta-schema v0.0.0-20201029221707-1b72ef2ea333 github.com/polydawn/refmt v0.89.0 github.com/prometheus/client_golang v1.14.0 + github.com/puzpuzpuz/xsync/v2 v2.4.0 github.com/raulk/clock v1.1.0 github.com/raulk/go-watchdog v1.3.0 github.com/stretchr/testify v1.8.2 diff --git a/go.sum b/go.sum index 80dcf1433..0a423f8a9 100644 --- a/go.sum +++ b/go.sum @@ -1484,6 +1484,8 @@ github.com/prometheus/procfs v0.8.0 h1:ODq8ZFEaYeCaZOJlZZdJA2AbQR98dSHSM1KW/You5 github.com/prometheus/procfs v0.8.0/go.mod h1:z7EfXMXOkbkqb9IINtpCn86r/to3BnA0uaxHdg830/4= github.com/prometheus/statsd_exporter v0.21.0 h1:hA05Q5RFeIjgwKIYEdFd59xu5Wwaznf33yKI+pyX6T8= github.com/prometheus/statsd_exporter v0.21.0/go.mod h1:rbT83sZq2V+p73lHhPZfMc3MLCHmSHelCh9hSGYNLTQ= +github.com/puzpuzpuz/xsync/v2 v2.4.0 h1:5sXAMHrtx1bg9nbRZTOn8T4MkWe5V+o8yKRH02Eznag= +github.com/puzpuzpuz/xsync/v2 v2.4.0/go.mod h1:gD2H2krq/w52MfPLE+Uy64TzJDVY7lP2znR9qmR35kU= github.com/quic-go/qpack v0.4.0 h1:Cr9BXA1sQS2SmDUWjSofMPNKmvF6IiIfDRmgU0w1ZCo= github.com/quic-go/qpack v0.4.0/go.mod h1:UZVnYIfi5GRk+zI9UMaCPsmZ2xKJP7XBUvVyT1Knj9A= github.com/quic-go/qtls-go1-19 v0.2.1 h1:aJcKNMkH5ASEJB9FXNeZCyTEIHU1J7MmHyz1Q1TSG1A= diff --git a/lib/shardedmutex/shardedmutex.go b/lib/shardedmutex/shardedmutex.go new file mode 100644 index 000000000..47b677f51 --- /dev/null +++ b/lib/shardedmutex/shardedmutex.go @@ -0,0 +1,75 @@ +package shardedmutex + +import ( + "hash/maphash" + "sync" +) + +const cacheline = 64 + +// padding a mutex to a cacheline improves performance as the cachelines are not contested +// name old time/op new time/op delta +// Locks-8 74.6ns ± 7% 12.3ns ± 2% -83.54% (p=0.000 n=20+18) +type paddedMutex struct { + mt sync.Mutex + pad [cacheline - 8]uint8 +} + +type ShardedMutex struct { + shards []paddedMutex +} + +// New creates a new ShardedMutex with N shards +func New(n_shards int) ShardedMutex { + if n_shards < 1 { + panic("n_shards cannot be less than 1") + } + return ShardedMutex{ + shards: make([]paddedMutex, n_shards), + } +} + +func (sm ShardedMutex) Shards() int { + return len(sm.shards) +} + +func (sm ShardedMutex) Lock(shard int) { + sm.shards[shard].mt.Lock() +} + +func (sm ShardedMutex) Unlock(shard int) { + sm.shards[shard].mt.Unlock() +} + +func (sm ShardedMutex) GetLock(shard int) sync.Locker { + return &sm.shards[shard].mt +} + +type ShardedMutexFor[K any] struct { + inner ShardedMutex + + hasher func(maphash.Seed, K) uint64 + seed maphash.Seed +} + +func NewFor[K any](hasher func(maphash.Seed, K) uint64, n_shards int) ShardedMutexFor[K] { + return ShardedMutexFor[K]{ + inner: New(n_shards), + hasher: hasher, + seed: maphash.MakeSeed(), + } +} + +func (sm ShardedMutexFor[K]) shardFor(key K) int { + return int(sm.hasher(sm.seed, key) % uint64(len(sm.inner.shards))) +} + +func (sm ShardedMutexFor[K]) Lock(key K) { + sm.inner.Lock(sm.shardFor(key)) +} +func (sm ShardedMutexFor[K]) Unlock(key K) { + sm.inner.Unlock(sm.shardFor(key)) +} +func (sm ShardedMutexFor[K]) GetLock(key K) sync.Locker { + return sm.inner.GetLock(sm.shardFor(key)) +} diff --git a/lib/shardedmutex/shardedmutex_test.go b/lib/shardedmutex/shardedmutex_test.go new file mode 100644 index 000000000..a7d5f7d1d --- /dev/null +++ b/lib/shardedmutex/shardedmutex_test.go @@ -0,0 +1,159 @@ +package shardedmutex + +import ( + "fmt" + "hash/maphash" + "runtime" + "sync" + "sync/atomic" + "testing" + "time" +) + +func TestLockingDifferentShardsDoesNotBlock(t *testing.T) { + shards := 16 + sm := New(shards) + done := make(chan struct{}) + go func() { + select { + case <-done: + return + case <-time.After(5 * time.Second): + panic("test locked up") + } + }() + for i := 0; i < shards; i++ { + sm.Lock(i) + } + + close(done) +} +func TestLockingSameShardsBlocks(t *testing.T) { + shards := 16 + sm := New(shards) + wg := sync.WaitGroup{} + wg.Add(shards) + ch := make(chan int, shards) + + for i := 0; i < shards; i++ { + go func(i int) { + if i != 15 { + sm.Lock(i) + } + wg.Done() + wg.Wait() + sm.Lock((15 + i) % shards) + ch <- i + sm.Unlock(i) + }(i) + } + + wg.Wait() + for i := 0; i < 2*shards; i++ { + runtime.Gosched() + } + for i := 0; i < shards; i++ { + if a := <-ch; a != i { + t.Errorf("got %d instead of %d", a, i) + } + } +} + +func TestShardedByString(t *testing.T) { + shards := 16 + sm := NewFor(maphash.String, shards) + + wg1 := sync.WaitGroup{} + wg1.Add(shards * 20) + wg2 := sync.WaitGroup{} + wg2.Add(shards * 20) + + active := atomic.Int32{} + max := atomic.Int32{} + + for i := 0; i < shards*20; i++ { + go func(i int) { + wg1.Done() + wg1.Wait() + sm.Lock(fmt.Sprintf("goroutine %d", i)) + activeNew := active.Add(1) + for { + curMax := max.Load() + if curMax >= activeNew { + break + } + if max.CompareAndSwap(curMax, activeNew) { + break + } + } + for j := 0; j < 100; j++ { + runtime.Gosched() + } + active.Add(-1) + sm.Unlock(fmt.Sprintf("goroutine %d", i)) + wg2.Done() + }(i) + } + + wg2.Wait() + + if max.Load() != 16 { + t.Fatal("max load not achieved", max.Load()) + } + +} + +func BenchmarkShardedMutex(b *testing.B) { + shards := 16 + sm := New(shards) + + done := atomic.Int32{} + go func() { + for { + sm.Lock(0) + sm.Unlock(0) + if done.Load() != 0 { + return + } + } + }() + for i := 0; i < 100; i++ { + runtime.Gosched() + } + + b.ResetTimer() + for i := 0; i < b.N; i++ { + sm.Lock(1) + sm.Unlock(1) + } + done.Add(1) +} + +func BenchmarkShardedMutexOf(b *testing.B) { + shards := 16 + sm := NewFor(maphash.String, shards) + + str1 := "string1" + str2 := "string2" + + done := atomic.Int32{} + go func() { + for { + sm.Lock(str1) + sm.Unlock(str1) + if done.Load() != 0 { + return + } + } + }() + for i := 0; i < 100; i++ { + runtime.Gosched() + } + + b.ResetTimer() + for i := 0; i < b.N; i++ { + sm.Lock(str2) + sm.Unlock(str2) + } + done.Add(1) +}