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reduce copying

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This commit is contained in:
Jay Wren 2025-11-11 14:51:53 -05:00
parent cd5da73e73
commit 08d3502613
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2 changed files with 48 additions and 8 deletions
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10
interface.go
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@ -304,7 +304,10 @@ func (f *Interface) listenIn(reader io.ReadWriteCloser, i int) {
func (f *Interface) listenInSingle(reader io.ReadWriteCloser, i int) {
packet := make([]byte, mtu)
out := make([]byte, mtu)
// Allocate out buffer with virtio header headroom (10 bytes) to avoid copies on write
const virtioNetHdrLen = 10
outBuf := make([]byte, virtioNetHdrLen+mtu)
out := outBuf[virtioNetHdrLen:] // Use slice starting after headroom
fwPacket := &firewall.Packet{}
nb := make([]byte, 12, 12)
@ -328,6 +331,7 @@ func (f *Interface) listenInSingle(reader io.ReadWriteCloser, i int) {
func (f *Interface) listenInBatch(reader io.ReadWriteCloser, batchReader BatchReader, i int) {
batchSize := batchReader.BatchSize()
const virtioNetHdrLen = 10
// Allocate buffers for batch reading
bufs := make([][]byte, batchSize)
@ -337,7 +341,9 @@ func (f *Interface) listenInBatch(reader io.ReadWriteCloser, batchReader BatchRe
sizes := make([]int, batchSize)
// Per-packet state (reused across batches)
out := make([]byte, mtu)
// Allocate out buffer with virtio header headroom to avoid copies on write
outBuf := make([]byte, virtioNetHdrLen+mtu)
out := outBuf[virtioNetHdrLen:]
fwPacket := &firewall.Packet{}
nb := make([]byte, 12, 12)

46
overlay/tun_linux.go
View file

@ -92,9 +92,24 @@ func (w *wgDeviceWrapper) Read(b []byte) (int, error) {
}
func (w *wgDeviceWrapper) Write(b []byte) (int, error) {
// Allocate buffer with space for virtio header
buf := make([]byte, virtioNetHdrLen+len(b))
copy(buf[virtioNetHdrLen:], b)
// Check if buffer has the expected headroom pattern to avoid copy
var buf []byte
if cap(b) >= len(b)+virtioNetHdrLen {
buf = b[:cap(b)]
if len(buf) == len(b)+virtioNetHdrLen {
// Perfect! Buffer has headroom, no copy needed
buf = buf[:len(b)+virtioNetHdrLen]
} else {
// Unexpected capacity, safer to copy
buf = make([]byte, virtioNetHdrLen+len(b))
copy(buf[virtioNetHdrLen:], b)
}
} else {
// No headroom, need to allocate and copy
buf = make([]byte, virtioNetHdrLen+len(b))
copy(buf[virtioNetHdrLen:], b)
}
bufs := [][]byte{buf}
n, err := w.dev.Write(bufs, virtioNetHdrLen)
@ -408,9 +423,28 @@ func (t *tun) BatchSize() int {
func (t *tun) Write(b []byte) (int, error) {
if t.wgDevice != nil {
// Use wireguard device which handles virtio headers internally
// Allocate buffer with space for virtio header
buf := make([]byte, virtioNetHdrLen+len(b))
copy(buf[virtioNetHdrLen:], b)
// Check if buffer has the expected headroom pattern:
// cap(b) should be len(b) + virtioNetHdrLen, indicating pre-allocated headroom
var buf []byte
if cap(b) >= len(b)+virtioNetHdrLen {
// Buffer likely has headroom - use unsafe to access it
// Create a slice that includes the headroom by re-slicing from capacity
buf = b[:cap(b)]
// Check if we have exactly the right amount of extra capacity
if len(buf) == len(b)+virtioNetHdrLen {
// Perfect! This buffer was allocated with headroom, no copy needed
buf = buf[:len(b)+virtioNetHdrLen]
} else {
// Unexpected capacity, safer to copy
buf = make([]byte, virtioNetHdrLen+len(b))
copy(buf[virtioNetHdrLen:], b)
}
} else {
// No headroom, need to allocate and copy
buf = make([]byte, virtioNetHdrLen+len(b))
copy(buf[virtioNetHdrLen:], b)
}
bufs := [][]byte{buf}
n, err := t.wgDevice.Write(bufs, virtioNetHdrLen)