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drop ECN support for this release

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This commit is contained in:
JackDoan
2026-07-31 13:38:16 -05:00
parent d3779b6a39
commit 93946faf7a
24 changed files with 148 additions and 1101 deletions
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udp/udp_linux_writebatch.go
+25 -90
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@@ -27,17 +27,17 @@ import (
// packet one element of bufs: a single UDP datagram. The unit of the
// returned written count.
// run consecutive packets planRun groups into one entry: same
// destination and outer ECN, equal sizes (a shorter packet only
// last), within maxGSOBytes and maxGSOSegments. Without GSO a run
// is always one packet. Runs are atomic: packed whole into one
// entry, or skipped whole if the socket cannot address their
// destination, leaving a hole (bufs indices covered by no entry).
// destination, equal sizes (a shorter packet only last), within
// maxGSOBytes and maxGSOSegments. Without GSO a run is always one
// packet. Runs are atomic: packed whole into one entry, or
// skipped whole if the socket cannot address their destination,
// leaving a hole (bufs indices covered by no entry).
// entry one mmsghdr slot of the sendmmsg array; the kernel's unit of
// success and failure. A multi-packet entry carries a UDP_SEGMENT
// cmsg and is sent as one superpacket the kernel segments into
// gso_size-byte datagrams. Entries never split.
// chunk the entries packed for one sendmmsg call, at most MaxWriteBatch.
// batch the caller's whole bufs/addrs/ecns triple, processed as one or
// batch the caller's whole bufs/addrs pair, processed as one or
// more chunks.
type batchWriter struct {
fd int
@@ -59,13 +59,10 @@ type batchWriter struct {
names [][]byte
// Per-entry cmsg scratch: one contiguous slab of
// MaxWriteBatch * cmsgSpace bytes holding two cmsg headers per entry
// (UDP_SEGMENT, then IP_TOS / IPV6_TCLASS). Layout in
// prepareWriteMessages.
cmsg []byte
cmsgSpace int
cmsgSegSpace int
cmsgEcnSpace int
// MaxWriteBatch * cmsgSpace bytes holding one UDP_SEGMENT cmsg per
// entry. Layout in prepareWriteMessages.
cmsg []byte
cmsgSpace int
// entryEnd[e] is the bufs index after the last packet packed into entry
// e. entryEnd[e]-entryPkts[e] recovers the bufs index the entry's run
@@ -91,17 +88,11 @@ func newBatchWriter(fd int, isV4 bool, l *slog.Logger) *batchWriter {
// prepareWriteMessages allocates the per-entry mmsghdr/iovec/sockaddr/cmsg
// scratch. Hdr.Iov/Iovlen/Control/Controllen are wired per call, since an
// entry spans a variable number of iovecs and may or may not carry cmsgs.
// entry spans a variable number of iovecs and may or may not carry a cmsg.
//
// Each entry's cmsg slot holds up to two headers at fixed offsets:
//
// [0 .. cmsgSegSpace) UDP_SEGMENT (gso_size, uint16)
// [cmsgSegSpace .. cmsgSpace) IP_TOS or IPV6_TCLASS (int32)
//
// The UDP_SEGMENT header is pre-filled here; only its payload is rewritten
// per call. The ECN header is written per entry by writeEntryCmsg because
// its Level/Type follow the destination's family. Hdr.Control/Controllen
// select whichever subset applies (none / segment / ecn / both).
// Each entry's cmsg slot holds one UDP_SEGMENT (gso_size, uint16) header,
// pre-filled here; only its payload is rewritten per call.
// Hdr.Control/Controllen select whether it applies (none / segment).
func (w *batchWriter) prepareWriteMessages(n int) {
w.msgs = make([]rawMessage, n)
w.iovs = make([]iovec, n)
@@ -109,9 +100,7 @@ func (w *batchWriter) prepareWriteMessages(n int) {
w.entryEnd = make([]int, n)
w.entryPkts = make([]int, n)
w.cmsgSegSpace = unix.CmsgSpace(2)
w.cmsgEcnSpace = unix.CmsgSpace(4)
w.cmsgSpace = w.cmsgSegSpace + w.cmsgEcnSpace
w.cmsgSpace = unix.CmsgSpace(2)
w.cmsg = make([]byte, n*w.cmsgSpace)
for k := 0; k < n; k++ {
@@ -197,13 +186,10 @@ func parseRelease(r string) (major, minor int) {
//
// Returns the number of packets sent. An error means the call itself
// failed; a short count means some destinations were undeliverable.
func (w *batchWriter) WriteBatch(bufs [][]byte, addrs []netip.AddrPort, ecns []byte) (int, error) {
func (w *batchWriter) WriteBatch(bufs [][]byte, addrs []netip.AddrPort) (int, error) {
if len(bufs) != len(addrs) {
return 0, fmt.Errorf("WriteBatch: len(bufs)=%d != len(addrs)=%d", len(bufs), len(addrs))
}
if ecns != nil && len(ecns) != len(bufs) {
return 0, fmt.Errorf("WriteBatch: len(ecns)=%d != len(bufs)=%d", len(ecns), len(bufs))
}
// Callers deliver same-destination packets contiguously and in counter order, so we run the GSO planner directly without a pre-sort.
// A sorting pass measurably hurt throughput in microbenchmarks while providing no observed reordering benefit.
@@ -221,7 +207,7 @@ func (w *batchWriter) WriteBatch(bufs [][]byte, addrs []netip.AddrPort, ecns []b
if iovBudget < 1 {
break
}
runLen, segSize := w.planRun(bufs, addrs, ecns, i, iovBudget)
runLen, segSize := w.planRun(bufs, addrs, i, iovBudget)
if runLen == 0 {
break
}
@@ -254,13 +240,7 @@ func (w *batchWriter) WriteBatch(bufs [][]byte, addrs []netip.AddrPort, ecns []b
setMsgIovlen(hdr, runLen)
hdr.Namelen = uint32(nlen)
var ecn byte
if ecns != nil {
ecn = ecns[i]
}
// ECN cmsg family follows the destination, not the socket
dstIsV4 := addrs[i].Addr().Unmap().Is4()
w.writeEntryCmsg(entry, runLen, segSize, ecn, dstIsV4)
w.writeEntryCmsg(entry, runLen, segSize)
i += runLen
iovIdx += runLen
@@ -340,9 +320,8 @@ func (w *batchWriter) WriteBatch(bufs [][]byte, addrs []netip.AddrPort, ecns []b
// planRun returns the length of the run starting at start and its segment
// size (len(bufs[start])). A run of length 1 carries no UDP_SEGMENT cmsg
// and is sent as a plain datagram; without GSO support planRun always
// returns 1. Outer ECN is a run boundary: the kernel stamps one codepoint per entry.
func (w *batchWriter) planRun(bufs [][]byte, addrs []netip.AddrPort, ecns []byte, start, iovBudget int) (int, int) {
// and is sent as a plain datagram; without GSO support planRun always returns 1.
func (w *batchWriter) planRun(bufs [][]byte, addrs []netip.AddrPort, start, iovBudget int) (int, int) {
if start >= len(bufs) || iovBudget < 1 {
return 0, 0
}
@@ -351,10 +330,6 @@ func (w *batchWriter) planRun(bufs [][]byte, addrs []netip.AddrPort, ecns []byte
return 1, segSize
}
dst := addrs[start]
var ecn byte
if ecns != nil {
ecn = ecns[start]
}
maxLen := w.maxGSOSegments
if iovBudget < maxLen {
maxLen = iovBudget
@@ -369,9 +344,6 @@ func (w *batchWriter) planRun(bufs [][]byte, addrs []netip.AddrPort, ecns []byte
if addrs[start+runLen] != dst {
break
}
if ecns != nil && ecns[start+runLen] != ecn {
break
}
if total+nextLen > maxGSOBytes {
break
}
@@ -385,55 +357,18 @@ func (w *batchWriter) planRun(bufs [][]byte, addrs []netip.AddrPort, ecns []byte
return runLen, segSize
}
// writeECNCmsg fills the start of buf with one IP_TOS / IPV6_TCLASS cmsg
// carrying the 2-bit ECN codepoint. buf must be cmsg-aligned (the batch
// writer's heap slab is runtime-aligned; sendmsg passes uint64-backed stack
// scratch) and at least CmsgSpace(4) bytes. The cmsg family must match the
// socket: on the default dual-stack v6 bind, a v4-mapped destination takes
// the kernel's IPv4 path, which reads IP_TOS and ignores IPV6_TCLASS. The
// payload is a 4-byte int for both families, so the cmsg space is the same.
func writeECNCmsg(buf []byte, dstIsV4 bool, ecn byte) {
h := (*unix.Cmsghdr)(unsafe.Pointer(&buf[0]))
if dstIsV4 {
h.Level = int32(unix.IPPROTO_IP)
h.Type = int32(unix.IP_TOS)
} else {
h.Level = int32(unix.IPPROTO_IPV6)
h.Type = int32(unix.IPV6_TCLASS)
}
setCmsgLen(h, unix.CmsgLen(4))
dataOff := unix.CmsgLen(0)
binary.NativeEndian.PutUint32(buf[dataOff:dataOff+4], uint32(ecn))
}
// writeEntryCmsg writes one entry's cmsgs: the UDP_SEGMENT payload when
// runLen >= 2, the IP_TOS/IPV6_TCLASS cmsg when ecn != 0, then points
// Hdr.Control at the smallest span covering the cmsgs in use.
func (w *batchWriter) writeEntryCmsg(entry, runLen, segSize int, ecn byte, dstIsV4 bool) {
// writeEntryCmsg writes one entry's UDP_SEGMENT payload when runLen >= 2 and
// points Hdr.Control at it; a single-packet entry carries no cmsg.
func (w *batchWriter) writeEntryCmsg(entry, runLen, segSize int) {
hdr := &w.msgs[entry].Hdr
useSeg := runLen >= 2
useEcn := ecn != 0
base := entry * w.cmsgSpace
if useSeg {
if runLen >= 2 {
dataOff := base + unix.CmsgLen(0)
binary.NativeEndian.PutUint16(w.cmsg[dataOff:dataOff+2], uint16(segSize))
}
if useEcn {
writeECNCmsg(w.cmsg[base+w.cmsgSegSpace:], dstIsV4, ecn)
}
switch {
case useSeg && useEcn:
hdr.Control = &w.cmsg[base]
setMsgControllen(hdr, w.cmsgSpace)
case useSeg:
hdr.Control = &w.cmsg[base]
setMsgControllen(hdr, w.cmsgSegSpace)
case useEcn:
hdr.Control = &w.cmsg[base+w.cmsgSegSpace]
setMsgControllen(hdr, w.cmsgEcnSpace)
default:
} else {
hdr.Control = nil
setMsgControllen(hdr, 0)
}