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wgengine/magicsock: drop DERP queue from head rather than tail

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If the DERP queue is full, drop the oldest item first, rather than the
youngest, on the assumption that older data is more likely to be
unanswerable.

Updates tailscale/corp#31762

Signed-off-by: James Tucker <james@tailscale.com>
This commit is contained in:
James Tucker
2025-08-28 21:29:11 -07:00
committed by James Tucker
parent 89fe2e1f12
commit 3b68d607be
2 changed files with 23 additions and 13 deletions
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4
wgengine/magicsock/derp.go
View File

@@ -91,7 +91,7 @@ func (c *Conn) fallbackDERPRegionForPeer(peer key.NodePublic) (regionID int) {
type activeDerp struct {
c *derphttp.Client
cancel context.CancelFunc
writeCh chan<- derpWriteRequest
writeCh chan derpWriteRequest
// lastWrite is the time of the last request for its write
// channel (currently even if there was no write).
// It is always non-nil and initialized to a non-zero Time.
@@ -302,7 +302,7 @@ const derpWriteQueueDepth = 32
//
// It returns nil if the network is down, the Conn is closed, or the regionID is
// not known.
func (c *Conn) derpWriteChanForRegion(regionID int, peer key.NodePublic) chan<- derpWriteRequest {
func (c *Conn) derpWriteChanForRegion(regionID int, peer key.NodePublic) chan derpWriteRequest {
if c.networkDown() {
return nil
}

32
wgengine/magicsock/magicsock.go
View File

@@ -1642,18 +1642,27 @@ func (c *Conn) sendAddr(addr netip.AddrPort, pubKey key.NodePublic, b []byte, is
// internal locks.
pkt := bytes.Clone(b)
select {
case <-c.donec:
metricSendDERPErrorClosed.Add(1)
return false, errConnClosed
case ch <- derpWriteRequest{addr, pubKey, pkt, isDisco}:
metricSendDERPQueued.Add(1)
return true, nil
default:
metricSendDERPErrorQueue.Add(1)
// Too many writes queued. Drop packet.
return false, errDropDerpPacket
wr := derpWriteRequest{addr, pubKey, pkt, isDisco}
for range 3 {
select {
case <-c.donec:
metricSendDERPErrorClosed.Add(1)
return false, errConnClosed
case ch <- wr:
metricSendDERPQueued.Add(1)
return true, nil
default:
select {
case <-ch:
metricSendDERPDropped.Add(1)
default:
}
}
}
// gave up after 3 write attempts
metricSendDERPErrorQueue.Add(1)
// Too many writes queued. Drop packet.
return false, errDropDerpPacket
}
type receiveBatch struct {
@@ -3937,6 +3946,7 @@ var (
metricSendDERPErrorChan = clientmetric.NewCounter("magicsock_send_derp_error_chan")
metricSendDERPErrorClosed = clientmetric.NewCounter("magicsock_send_derp_error_closed")
metricSendDERPErrorQueue = clientmetric.NewCounter("magicsock_send_derp_error_queue")
metricSendDERPDropped = clientmetric.NewCounter("magicsock_send_derp_dropped")
metricSendUDP = clientmetric.NewAggregateCounter("magicsock_send_udp")
metricSendUDPError = clientmetric.NewCounter("magicsock_send_udp_error")
metricSendPeerRelay = clientmetric.NewAggregateCounter("magicsock_send_peer_relay")