optimize: calc size, use values

note that this splits a mutex access in two

wgengine/userspace.go

@@ -921,11 +921,6 @@ func (e *userspaceEngine) getStatus() (*Status, error) {
 		errc <- err
 	}()
 
-	pp := make(map[wgkey.Key]*ipnstate.PeerStatusLite)
-	p := &ipnstate.PeerStatusLite{}
-
-	var hst1, hst2, n int64
-
 	br := e.statusBufioReader
 	if br != nil {
 		br.Reset(pr)
@@ -933,6 +928,29 @@ func (e *userspaceEngine) getStatus() (*Status, error) {
 		br = bufio.NewReaderSize(pr, 1<<10)
 		e.statusBufioReader = br
 	}
+
+	peers, err := e.getPeerStatusLite(br)
+	if err != nil {
+		return nil, err
+	}
+	if err := <-errc; err != nil {
+		return nil, fmt.Errorf("IpcGetOperation: %v", err)
+	}
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	return &Status{
+		LocalAddrs: append([]tailcfg.Endpoint(nil), e.endpoints...),
+		Peers:      peers,
+		DERPs:      derpConns,
+	}, nil
+}
+
+func (e *userspaceEngine) getPeerStatusLite(br *bufio.Reader) ([]ipnstate.PeerStatusLite, error) {
+	pp := make(map[wgkey.Key]ipnstate.PeerStatusLite)
+	var p ipnstate.PeerStatusLite
+
+	var hst1, hst2, n int64
+
 	for {
 		line, err := br.ReadSlice('\n')
 		if err == io.EOF {
@@ -954,11 +972,10 @@ func (e *userspaceEngine) getStatus() (*Status, error) {
 			if err != nil {
 				return nil, fmt.Errorf("IpcGetOperation: invalid key in line %q", line)
 			}
-			p = &ipnstate.PeerStatusLite{}
-			pp[wgkey.Key(pk)] = p
-
-			key := tailcfg.NodeKey(pk)
-			p.NodeKey = key
+			if !p.NodeKey.IsZero() {
+				pp[wgkey.Key(p.NodeKey)] = p
+			}
+			p = ipnstate.PeerStatusLite{NodeKey: tailcfg.NodeKey(pk)}
 		case "rx_bytes":
 			n, err = mem.ParseInt(v, 10, 64)
 			p.RxBytes = n
@@ -986,25 +1003,29 @@ func (e *userspaceEngine) getStatus() (*Status, error) {
 			} // else leave at time.IsZero()
 		}
 	}
-	if err := <-errc; err != nil {
-		return nil, fmt.Errorf("IpcGetOperation: %v", err)
+	if !p.NodeKey.IsZero() {
+		pp[wgkey.Key(p.NodeKey)] = p
 	}
 
 	e.mu.Lock()
 	defer e.mu.Unlock()
 
-	var peers []ipnstate.PeerStatusLite
+	// Do two passes, one to calculate size and the other to populate.
+	// This code is sensitive to allocations.
+	npeers := 0
 	for _, pk := range e.peerSequence {
-		if p, ok := pp[pk]; ok { // ignore idle ones not in wireguard-go's config
-			peers = append(peers, *p)
+		if _, ok := pp[pk]; ok { // ignore idle ones not in wireguard-go's config
+			npeers++
 		}
 	}
 
-	return &Status{
-		LocalAddrs: append([]tailcfg.Endpoint(nil), e.endpoints...),
-		Peers:      peers,
-		DERPs:      derpConns,
-	}, nil
+	peers := make([]ipnstate.PeerStatusLite, 0, npeers)
+	for _, pk := range e.peerSequence {
+		if p, ok := pp[pk]; ok { // ignore idle ones not in wireguard-go's config
+			peers = append(peers, p)
+		}
+	}
+	return peers, nil
 }
 
 func (e *userspaceEngine) RequestStatus() {

wgengine/userspace_test.go

@@ -5,9 +5,11 @@
 package wgengine
 
 import (
+	"bufio"
 	"bytes"
 	"fmt"
 	"reflect"
+	"strings"
 	"testing"
 
 	"go4.org/mem"
@@ -17,6 +19,7 @@ import (
 	"tailscale.com/tailcfg"
 	"tailscale.com/tstime/mono"
 	"tailscale.com/types/key"
+	"tailscale.com/types/wgkey"
 	"tailscale.com/wgengine/router"
 	"tailscale.com/wgengine/wgcfg"
 )
@@ -252,3 +255,67 @@ func BenchmarkGenLocalAddrFunc(b *testing.B) {
 	})
 	b.Logf("x = %v", x)
 }
+
+func BenchmarkGetPeerStatusLite(b *testing.B) {
+	e := new(userspaceEngine)
+	br := bufio.NewReaderSize(nil, 1<<10)
+	parseKey := func(s string) wgkey.Key {
+		k, err := wgkey.ParseHex(s)
+		if err != nil {
+			b.Fatal(err)
+		}
+		return k
+	}
+	e.peerSequence = []wgkey.Key{
+		parseKey("0000000000000000000000000000000000000000000000000000000000000002"),
+		parseKey("0000000000000000000000000000000000000000000000000000000000000003"),
+		parseKey("0000000000000000000000000000000000000000000000000000000000000004"),
+	}
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		br.Reset(strings.NewReader(sampleStatus))
+		_, err := e.getPeerStatusLite(br)
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
+const sampleStatus = `
+private_key=0000000000000000000000000000000000000000000000000000000000000001
+listen_port=50818
+public_key=0000000000000000000000000000000000000000000000000000000000000002
+preshared_key=0000000000000000000000000000000000000000000000000000000000000000
+protocol_version=1
+endpoint={"pk":"0000000000000000000000000000000000000000000000000000000000000002","dk":"discokey:0000000000000000000000000000000000000000000000000000000000000000","ipp":["139.162.81.125:41641"]}
+last_handshake_time_sec=1628288511
+last_handshake_time_nsec=993469000
+tx_bytes=272
+rx_bytes=272
+persistent_keepalive_interval=25
+allowed_ip=100.100.100.101/32
+allowed_ip=::2/128
+public_key=0000000000000000000000000000000000000000000000000000000000000003
+preshared_key=0000000000000000000000000000000000000000000000000000000000000000
+protocol_version=1
+endpoint={"pk":"0000000000000000000000000000000000000000000000000000000000000003","dk":"discokey:c6c0a1488ac6cb9e0103d056ca51387e33513d577b985e77c6ea075f76b27d35","ipp":null}
+last_handshake_time_sec=1628288511
+last_handshake_time_nsec=615842000
+tx_bytes=1300
+rx_bytes=92
+persistent_keepalive_interval=0
+allowed_ip=100.100.100.102/32
+allowed_ip=::3/128
+public_key=0000000000000000000000000000000000000000000000000000000000000004
+preshared_key=0000000000000000000000000000000000000000000000000000000000000000
+protocol_version=1
+endpoint={"pk":"0000000000000000000000000000000000000000000000000000000000000004","dk":"discokey:c6c0a1488ac6cb9e0103d056ca51387e33513d577b985e77c6ea075f76b27d35","ipp":null}
+last_handshake_time_sec=1628288511
+last_handshake_time_nsec=615842000
+tx_bytes=1300
+rx_bytes=92
+persistent_keepalive_interval=0
+allowed_ip=100.100.100.103/32
+allowed_ip=::4/128
+`