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286 lines
9.9 KiB
286 lines
9.9 KiB
package p2p
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import (
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"sort"
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"strconv"
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"github.com/gogo/protobuf/proto"
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"github.com/tendermint/tendermint/libs/log"
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tmsync "github.com/tendermint/tendermint/libs/sync"
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)
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const defaultCapacity uint = 1048576 // 1MB
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// wrappedEnvelope wraps a p2p Envelope with its precomputed size.
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type wrappedEnvelope struct {
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envelope Envelope
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size uint
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}
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// assert the WDDR scheduler implements the queue interface at compile-time
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var _ queue = (*wdrrScheduler)(nil)
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// wdrrQueue implements a Weighted Deficit Round Robin (WDRR) scheduling
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// algorithm via the queue interface. A WDRR queue is created per peer, where
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// the queue will have N number of flows. Each flow corresponds to a p2p Channel,
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// so there are n input flows and a single output source, the peer's connection.
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//
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// The WDRR scheduler contains a shared buffer with a fixed capacity.
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//
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// Each flow has the following:
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// - quantum: The number of bytes that is added to the deficit counter of the
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// flow in each round. The flow can send at most quantum bytes at a time. Each
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// flow has its own unique quantum, which gives the queue its weighted nature.
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// A higher quantum corresponds to a higher weight/priority. The quantum is
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// computed as MaxSendBytes * Priority.
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// - deficit counter: The number of bytes that the flow is allowed to transmit
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// when it is its turn.
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//
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// See: https://en.wikipedia.org/wiki/Deficit_round_robin
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type wdrrScheduler struct {
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logger log.Logger
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metrics *Metrics
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chDescs []ChannelDescriptor
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capacity uint
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size uint
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chPriorities map[ChannelID]uint
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buffer map[ChannelID][]wrappedEnvelope
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quanta map[ChannelID]uint
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deficits map[ChannelID]uint
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closer *tmsync.Closer
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doneCh *tmsync.Closer
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enqueueCh chan Envelope
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dequeueCh chan Envelope
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}
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func newWDRRScheduler(
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logger log.Logger,
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m *Metrics,
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chDescs []ChannelDescriptor,
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enqueueBuf, dequeueBuf, capacity uint,
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) *wdrrScheduler {
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// copy each ChannelDescriptor and sort them by channel priority
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chDescsCopy := make([]ChannelDescriptor, len(chDescs))
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copy(chDescsCopy, chDescs)
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sort.Slice(chDescsCopy, func(i, j int) bool { return chDescsCopy[i].Priority > chDescsCopy[j].Priority })
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var (
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buffer = make(map[ChannelID][]wrappedEnvelope)
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chPriorities = make(map[ChannelID]uint)
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quanta = make(map[ChannelID]uint)
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deficits = make(map[ChannelID]uint)
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)
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for _, chDesc := range chDescsCopy {
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chID := ChannelID(chDesc.ID)
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chPriorities[chID] = uint(chDesc.Priority)
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buffer[chID] = make([]wrappedEnvelope, 0)
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quanta[chID] = chDesc.MaxSendBytes * uint(chDesc.Priority)
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}
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return &wdrrScheduler{
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logger: logger.With("queue", "wdrr"),
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metrics: m,
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capacity: capacity,
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chPriorities: chPriorities,
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chDescs: chDescsCopy,
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buffer: buffer,
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quanta: quanta,
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deficits: deficits,
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closer: tmsync.NewCloser(),
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doneCh: tmsync.NewCloser(),
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enqueueCh: make(chan Envelope, enqueueBuf),
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dequeueCh: make(chan Envelope, dequeueBuf),
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}
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}
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// enqueue returns an unbuffered write-only channel which a producer can send on.
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func (s *wdrrScheduler) enqueue() chan<- Envelope {
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return s.enqueueCh
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}
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// dequeue returns an unbuffered read-only channel which a consumer can read from.
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func (s *wdrrScheduler) dequeue() <-chan Envelope {
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return s.dequeueCh
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}
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func (s *wdrrScheduler) closed() <-chan struct{} {
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return s.closer.Done()
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}
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// close closes the WDRR queue. After this call enqueue() will block, so the
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// caller must select on closed() as well to avoid blocking forever. The
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// enqueue() and dequeue() along with the internal channels will NOT be closed.
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// Note, close() will block until all externally spawned goroutines have exited.
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func (s *wdrrScheduler) close() {
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s.closer.Close()
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<-s.doneCh.Done()
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}
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// start starts the WDRR queue process in a blocking goroutine. This must be
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// called before the queue can start to process and accept Envelopes.
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func (s *wdrrScheduler) start() {
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go s.process()
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}
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// process starts a blocking WDRR scheduler process, where we continuously
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// evaluate if we need to attempt to enqueue an Envelope or schedule Envelopes
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// to be dequeued and subsequently read and sent on the source connection.
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// Internally, each p2p Channel maps to a flow, where each flow has a deficit
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// and a quantum.
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//
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// For each Envelope requested to be enqueued, we evaluate if there is sufficient
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// capacity in the shared buffer to add the Envelope. If so, it is added.
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// Otherwise, we evaluate all flows of lower priority where we attempt find an
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// existing Envelope in the shared buffer of sufficient size that can be dropped
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// in place of the incoming Envelope. If there is no such Envelope that can be
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// dropped, then the incoming Envelope is dropped.
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//
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// When there is nothing to be enqueued, we perform the WDRR algorithm and
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// determine which Envelopes can be dequeued. For each Envelope that can be
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// dequeued, it is sent on the dequeueCh. Specifically, for each flow, if it is
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// non-empty, its deficit counter is incremented by its quantum value. Then, the
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// value of the deficit counter is a maximal amount of bytes that can be sent at
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// this round. If the deficit counter is greater than the Envelopes's message
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// size at the head of the queue (HoQ), this envelope can be sent and the value
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// of the counter is decremented by the message's size. Then, the size of the
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// next Envelopes's message is compared to the counter value, etc. Once the flow
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// is empty or the value of the counter is insufficient, the scheduler will skip
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// to the next flow. If the flow is empty, the value of the deficit counter is
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// reset to 0.
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//
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// XXX/TODO: Evaluate the single goroutine scheduler mechanism. In other words,
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// evaluate the effectiveness and performance of having a single goroutine
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// perform handling both enqueueing and dequeueing logic. Specifically, there
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// is potentially contention between reading off of enqueueCh and trying to
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// enqueue while also attempting to perform the WDRR algorithm and find the next
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// set of Envelope(s) to send on the dequeueCh. Alternatively, we could consider
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// separate scheduling goroutines, but then that requires the use of mutexes and
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// possibly a degrading performance.
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func (s *wdrrScheduler) process() {
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defer s.doneCh.Close()
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for {
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select {
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case <-s.closer.Done():
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return
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case e := <-s.enqueueCh:
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// attempt to enqueue the incoming Envelope
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chIDStr := strconv.Itoa(int(e.channelID))
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wEnv := wrappedEnvelope{envelope: e, size: uint(proto.Size(e.Message))}
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msgSize := wEnv.size
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s.metrics.PeerPendingSendBytes.With("peer_id", string(e.To)).Add(float64(msgSize))
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// If we're at capacity, we need to either drop the incoming Envelope or
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// an Envelope from a lower priority flow. Otherwise, we add the (wrapped)
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// envelope to the flow's queue.
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if s.size+wEnv.size > s.capacity {
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chPriority := s.chPriorities[e.channelID]
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var (
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canDrop bool
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dropIdx int
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dropChID ChannelID
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)
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// Evaluate all lower priority flows and determine if there exists an
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// Envelope that is of equal or greater size that we can drop in favor
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// of the incoming Envelope.
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for i := len(s.chDescs) - 1; i >= 0 && uint(s.chDescs[i].Priority) < chPriority && !canDrop; i-- {
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currChID := ChannelID(s.chDescs[i].ID)
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flow := s.buffer[currChID]
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for j := 0; j < len(flow) && !canDrop; j++ {
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if flow[j].size >= wEnv.size {
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canDrop = true
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dropIdx = j
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dropChID = currChID
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break
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}
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}
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}
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// If we can drop an existing Envelope, drop it and enqueue the incoming
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// Envelope.
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if canDrop {
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chIDStr = strconv.Itoa(int(dropChID))
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chPriority = s.chPriorities[dropChID]
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msgSize = s.buffer[dropChID][dropIdx].size
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// Drop Envelope for the lower priority flow and update the queue's
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// buffer size
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s.size -= msgSize
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s.buffer[dropChID] = append(s.buffer[dropChID][:dropIdx], s.buffer[dropChID][dropIdx+1:]...)
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// add the incoming Envelope and update queue's buffer size
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s.size += wEnv.size
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s.buffer[e.channelID] = append(s.buffer[e.channelID], wEnv)
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s.metrics.PeerQueueMsgSize.With("ch_id", chIDStr).Set(float64(wEnv.size))
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}
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// We either dropped the incoming Enevelope or one from an existing
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// lower priority flow.
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s.metrics.PeerQueueDroppedMsgs.With("ch_id", chIDStr).Add(1)
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s.logger.Debug(
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"dropped envelope",
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"ch_id", chIDStr,
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"priority", chPriority,
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"capacity", s.capacity,
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"msg_size", msgSize,
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)
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} else {
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// we have sufficient capacity to enqueue the incoming Envelope
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s.metrics.PeerQueueMsgSize.With("ch_id", chIDStr).Set(float64(wEnv.size))
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s.buffer[e.channelID] = append(s.buffer[e.channelID], wEnv)
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s.size += wEnv.size
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}
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default:
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// perform the WDRR algorithm
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for _, chDesc := range s.chDescs {
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chID := ChannelID(chDesc.ID)
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// only consider non-empty flows
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if len(s.buffer[chID]) > 0 {
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// bump flow's quantum
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s.deficits[chID] += s.quanta[chID]
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// grab the flow's current deficit counter and HoQ (wrapped) Envelope
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d := s.deficits[chID]
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we := s.buffer[chID][0]
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// While the flow is non-empty and we can send the current Envelope
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// on the dequeueCh:
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//
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// 1. send the Envelope
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// 2. update the scheduler's shared buffer's size
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// 3. update the flow's deficit
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// 4. remove from the flow's queue
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// 5. grab the next HoQ Envelope and flow's deficit
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for len(s.buffer[chID]) > 0 && d >= we.size {
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s.metrics.PeerSendBytesTotal.With("peer_id", string(we.envelope.To)).Add(float64(we.size))
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s.dequeueCh <- we.envelope
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s.size -= we.size
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s.deficits[chID] -= we.size
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s.buffer[chID] = s.buffer[chID][1:]
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if len(s.buffer[chID]) > 0 {
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d = s.deficits[chID]
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we = s.buffer[chID][0]
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}
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}
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}
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// reset the flow's deficit to zero if it is empty
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if len(s.buffer[chID]) == 0 {
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s.deficits[chID] = 0
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}
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}
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}
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}
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}
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