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derp: start adding flow tracking stats

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This starts adding flow tracking stats, without exposing them anywhere
yet. Flow structs are created as needed and metrics are bumped, and
benchmarks show no change in performance.

Updates #3560

Change-Id: I376187a8452ec92d49effcbf48a6fb4f4d787b8a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2024-09-15 08:56:16 -07:00
parent a8bd0cb9c2
commit fe830a744b
4 changed files with 290 additions and 34 deletions
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69
derp/derp_server.go
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@ -46,6 +46,7 @@
"tailscale.com/tstime/rate"
"tailscale.com/types/key"
"tailscale.com/types/logger"
"tailscale.com/util/lru"
"tailscale.com/util/mak"
"tailscale.com/util/set"
"tailscale.com/util/slicesx"
@ -156,6 +157,9 @@ type Server struct {
mu sync.Mutex
closed bool
flow map[flowKey]*flow
flows []*flow // slice of values of flow map
flowCleanIndex int
netConns map[Conn]chan struct{} // chan is closed when conn closes
clients map[key.NodePublic]*clientSet
watchers set.Set[*sclient] // mesh peers
@ -341,6 +345,7 @@ func NewServer(privateKey key.NodePrivate, logf logger.Logf) *Server {
packetsDroppedType: metrics.LabelMap{Label: "type"},
clients: map[key.NodePublic]*clientSet{},
clientsMesh: map[key.NodePublic]PacketForwarder{},
flow: map[flowKey]*flow{},
netConns: map[Conn]chan struct{}{},
memSys0: ms.Sys,
watchers: set.Set[*sclient]{},
@ -866,9 +871,20 @@ func (s *Server) debugLogf(format string, v ...any) {
}
}
// onRunLoopDone is called when the run loop is done
// to clean up.
//
// It must only be called from the [slient.run] goroutine.
func (c *sclient) onRunLoopDone() {
c.flows.ForEach(func(k key.NodePublic, peer flowAndClientSet) {
peer.f.ref.Add(-1)
})
}
// run serves the client until there's an error.
// If the client hangs up or the server is closed, run returns nil, otherwise run returns an error.
func (c *sclient) run(ctx context.Context) error {
defer c.onRunLoopDone()
// Launch sender, but don't return from run until sender goroutine is done.
var grp errgroup.Group
sendCtx, cancelSender := context.WithCancel(ctx)
@ -1028,6 +1044,7 @@ func (c *sclient) handleFrameForwardPacket(ft frameType, fl uint32) error {
var dst *sclient
s.mu.Lock()
flo := s.getMakeFlowLocked(srcKey, dstKey)
if set, ok := s.clients[dstKey]; ok {
dstLen = set.Len()
dst = set.activeClient.Load()
@ -1050,7 +1067,7 @@ func (c *sclient) handleFrameForwardPacket(ft frameType, fl uint32) error {
return c.sendPkt(dst, pkt{
bs: contents,
enqueuedAt: c.s.clock.Now(),
src: srcKey,
flow: flo,
})
}
@ -1063,22 +1080,13 @@ func (c *sclient) handleFrameSendPacket(ft frameType, fl uint32) error {
return fmt.Errorf("client %v: recvPacket: %v", c.key, err)
}
var fwd PacketForwarder
var dstLen int
var dst *sclient
s.mu.Lock()
if set, ok := s.clients[dstKey]; ok {
dstLen = set.Len()
dst = set.activeClient.Load()
}
if dst == nil && dstLen < 1 {
fwd = s.clientsMesh[dstKey]
}
s.mu.Unlock()
flo, dst, fwd := c.lookupDest(dstKey)
flo.noteActivity()
if dst == nil {
if fwd != nil {
flo.pktSendRegion.Add(1)
flo.byteSendRegion.Add(1)
s.packetsForwardedOut.Add(1)
err := fwd.ForwardPacket(c.key, dstKey, contents)
c.debugLogf("SendPacket for %s, forwarding via %s: %v", dstKey.ShortString(), fwd, err)
@ -1088,22 +1096,22 @@ func (c *sclient) handleFrameSendPacket(ft frameType, fl uint32) error {
}
return nil
}
flo.dropUnknownDest.Add(1)
reason := dropReasonUnknownDest
if dstLen > 1 {
reason = dropReasonDupClient
} else {
c.requestPeerGoneWriteLimited(dstKey, contents, PeerGoneReasonNotHere)
}
s.recordDrop(contents, c.key, dstKey, reason)
c.debugLogf("SendPacket for %s, dropping with reason=%s", dstKey.ShortString(), reason)
return nil
}
c.debugLogf("SendPacket for %s, sending directly", dstKey.ShortString())
flo.pktSendLocal.Add(1)
flo.byteSendLocal.Add(1)
p := pkt{
bs: contents,
enqueuedAt: c.s.clock.Now(),
src: c.key,
flow: flo,
}
return c.sendPkt(dst, p)
}
@ -1151,6 +1159,7 @@ func (s *Server) recordDrop(packetBytes []byte, srcKey, dstKey key.NodePublic, r
}
func (c *sclient) sendPkt(dst *sclient, p pkt) error {
// TODO(bradfitz): bump metrics on p.flow
s := c.s
dstKey := dst.key
@ -1511,6 +1520,7 @@ type sclient struct {
br *bufio.Reader
connectedAt time.Time
preferred bool
flows lru.Cache[key.NodePublic, flowAndClientSet] // keyed by dest
// Owned by sendLoop, not thread-safe.
sawSrc map[key.NodePublic]set.Handle
@ -1563,8 +1573,12 @@ type pkt struct {
// The memory is owned by pkt.
bs []byte
// src is the who's the sender of the packet.
src key.NodePublic
// flow is the flow stats from the src to the dest.
flow *flow
}
func (p pkt) src() key.NodePublic {
return p.flow.flowKey.Value().src
}
// peerGoneMsg is a request to write a peerGone frame to an sclient
@ -1635,14 +1649,13 @@ func (c *sclient) onSendLoopDone() {
for {
select {
case pkt := <-c.sendQueue:
c.s.recordDrop(pkt.bs, pkt.src, c.key, dropReasonGoneDisconnected)
c.s.recordDrop(pkt.bs, pkt.src(), c.key, dropReasonGoneDisconnected)
case pkt := <-c.discoSendQueue:
c.s.recordDrop(pkt.bs, pkt.src, c.key, dropReasonGoneDisconnected)
c.s.recordDrop(pkt.bs, pkt.src(), c.key, dropReasonGoneDisconnected)
default:
return
}
}
}
func (c *sclient) sendLoop(ctx context.Context) error {
@ -1669,11 +1682,11 @@ func (c *sclient) sendLoop(ctx context.Context) error {
werr = c.sendMeshUpdates()
continue
case msg := <-c.sendQueue:
werr = c.sendPacket(msg.src, msg.bs)
werr = c.sendPacket(msg.src(), msg.bs)
c.recordQueueTime(msg.enqueuedAt)
continue
case msg := <-c.discoSendQueue:
werr = c.sendPacket(msg.src, msg.bs)
werr = c.sendPacket(msg.src(), msg.bs)
c.recordQueueTime(msg.enqueuedAt)
continue
case msg := <-c.sendPongCh:
@ -1700,10 +1713,10 @@ func (c *sclient) sendLoop(ctx context.Context) error {
werr = c.sendMeshUpdates()
continue
case msg := <-c.sendQueue:
werr = c.sendPacket(msg.src, msg.bs)
werr = c.sendPacket(msg.src(), msg.bs)
c.recordQueueTime(msg.enqueuedAt)
case msg := <-c.discoSendQueue:
werr = c.sendPacket(msg.src, msg.bs)
werr = c.sendPacket(msg.src(), msg.bs)
c.recordQueueTime(msg.enqueuedAt)
case msg := <-c.sendPongCh:
werr = c.sendPong(msg)

182
derp/flow.go Normal file
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@ -0,0 +1,182 @@
// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package derp
import (
"sync/atomic"
"time"
"unique"
"tailscale.com/types/key"
)
type flowKey struct {
src, dst key.NodePublic
}
// flow tracks metadata about a directional flow of packets from a source
// node to a destination node. The public keys of the src is known
// by the caller.
type flow struct {
createdUnixNano int64 // int64 instead of time.Time to keep flow smaller
index int // index in Server.flows slice or -1 if not; guarded by Server.mu
flowKey unique.Handle[flowKey] // TODO: make this a unique handle of two unique handles for each NodePublic?
roughActivityUnixTime atomic.Int64 // unix sec of recent activity, updated at most once a minute
pktSendRegion atomic.Int64
byteSendRegion atomic.Int64
pktSendLocal atomic.Int64
byteSendLocal atomic.Int64
dropUnknownDest atomic.Int64 // no local or region client for dest
dropGone atomic.Int64
// ref is the reference count of things (*Server, *sclient) holding on
// to this flow. As of 2024-09-18 it is currently only informational
// and not used for anything. The Server adds/removes a ref count when
// it's remove from its map and each 0, 1 or more sclients for a given
// recently active flow also add/remove a ref count.
//
// This might be used in the future as an alternate Server.flow eviction
// strategy but for now it's just a debug tool. We do want to keep flow
// stats surviving a brief client disconnections, so we do want Server
// to keep at least a momentary ref count alive.
ref atomic.Int64
}
// noteActivity updates f.recentActivityUnixTime if it's been
// more than a minute.
func (f *flow) noteActivity() {
now := time.Now().Unix()
if now-f.roughActivityUnixTime.Load() > 60 {
f.roughActivityUnixTime.Store(now)
}
}
// getMakeFlow either gets or makes a new flow for the given source and
// destination nodes.
func (s *Server) getMakeFlow(src, dst key.NodePublic) *flow {
s.mu.Lock()
defer s.mu.Unlock()
return s.getMakeFlowLocked(src, dst)
}
func (s *Server) getMakeFlowLocked(src, dst key.NodePublic) *flow {
k := flowKey{src, dst}
f, ok := s.flow[k]
if ok {
return f
}
now := time.Now()
f = &flow{
createdUnixNano: now.UnixNano(),
index: len(s.flows),
flowKey: unique.Make(k),
}
f.roughActivityUnixTime.Store(now.Unix())
f.ref.Add(1) // for Server's ref in the s.flows map itself
// As penance for the one flow we're about to add to the map and slice
// above, check two old flows for removal. We roll around and around the
// flows slice, so this is a simple way to eventually check everything for
// removal before we double in size.
for range 2 {
s.maybeCleanOldFlowLocked()
}
s.flow[k] = f
s.flows = append(s.flows, f)
return f
}
func (s *Server) maybeCleanOldFlowLocked() {
if len(s.flows) == 0 {
return
}
s.flowCleanIndex++
if s.flowCleanIndex >= len(s.flows) {
s.flowCleanIndex = 0
}
f := s.flows[s.flowCleanIndex]
now := time.Now().Unix()
ageSec := now - f.roughActivityUnixTime.Load()
if ageSec > 3600 {
// No activity in an hour. Remove it.
delete(s.flow, f.flowKey.Value())
holeIdx := f.index
s.flows[holeIdx] = s.flows[len(s.flows)-1]
s.flows[holeIdx].index = holeIdx
s.flows = s.flows[:len(s.flows)-1]
f.ref.Add(-1)
return
}
}
type flowAndClientSet struct {
f *flow // always non-nil
cs *clientSet // may be nil if peer not connected/known
}
// lookupDest returns the flow (always non-nil) and sclient and/or
// PacketForwarder (at least one of which will be nil, possibly both) for the
// given destination node.
// It must only be called from the [sclient.run] goroutine.
func (c *sclient) lookupDest(dst key.NodePublic) (_ *flow, _ *sclient, fwd PacketForwarder) {
peer, ok := c.flows.GetOk(dst)
if ok && peer.cs != nil {
if c := peer.cs.activeClient.Load(); c != nil {
// Common case for hot flows within the same node: we know the
// clientSet and no mutex is needed.
return peer.f, c, nil
}
}
if peer.f == nil {
peer.f = c.s.getMakeFlow(c.key, dst)
peer.f.ref.Add(1)
// At least store the flow in the map, even if we don't find the
// clientSet later. In theory we could coallesce this map write with a
// possible one later, but they should be rare and uncontended so we
// don't care as of 2024-09-18.
c.flows.Set(dst, peer)
c.maybeCleanFlows()
}
srv := c.s
srv.mu.Lock()
set, ok := srv.clients[dst]
if ok {
if c := set.activeClient.Load(); c != nil {
srv.mu.Unlock()
peer.cs = set
c.flows.Set(dst, peer)
c.maybeCleanFlows()
return peer.f, c, nil
}
fwd = srv.clientsMesh[dst]
}
srv.mu.Unlock()
return peer.f, nil, fwd // fwd may be nil too
}
// maybeCleanFlows cleans the oldest element from the client flows cache if
// it's too big.
//
// It must only be called from the [sclient.run] goroutine.
func (c *sclient) maybeCleanFlows() {
const maxClientFlowTrack = 100
if c.flows.Len() <= maxClientFlowTrack {
return
}
oldest, _ := c.flows.OldestKey()
facs, ok := c.flows.PeekOk(oldest)
if !ok {
panic("lookupDest: OldestKey lied")
}
facs.f.ref.Add(-1)
c.flows.Delete(oldest)
}

52
derp/flow_test.go Normal file
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@ -0,0 +1,52 @@
package derp
import (
"testing"
"unique"
"go4.org/mem"
"tailscale.com/types/key"
)
func BenchmarkUnique(b *testing.B) {
var keys [100]key.NodePublic
for i := range keys {
keys[i] = key.NodePublicFromRaw32(mem.B([]byte{31: byte(i)}))
}
b.Run("raw", func(b *testing.B) {
m := map[flowKey]bool{}
for range b.N {
for _, k := range keys {
key := flowKey{k, k}
if _, ok := m[key]; !ok {
m[key] = true
}
}
}
})
b.Run("unique-tightmake", func(b *testing.B) {
m := map[unique.Handle[flowKey]]bool{}
for range b.N {
for _, k := range keys {
key := unique.Make(flowKey{k, k})
if _, ok := m[key]; !ok {
m[key] = true
}
}
}
})
b.Run("unique-makeonce", func(b *testing.B) {
m := map[unique.Handle[flowKey]]bool{}
ukeys := make([]unique.Handle[flowKey], len(keys))
for i, k := range keys {
ukeys[i] = unique.Make(flowKey{k, k})
}
for range b.N {
for _, key := range ukeys {
if _, ok := m[key]; !ok {
m[key] = true
}
}
}
})
}

9
util/lru/lru.go
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@ -133,6 +133,15 @@ func (c *Cache[K, V]) DeleteOldest() {
}
}
// OldestKey returns the oldest key, without bumping it to the head.
// If the cache is empty, it returns ok false.
func (c *Cache[K, V]) OldestKey() (key K, ok bool) {
if c.head == nil {
return key, false
}
return c.head.prev.key, true
}
// Len returns the number of items in the cache.
func (c *Cache[K, V]) Len() int { return len(c.lookup) }