removes redundant vector allocations before calling sendmmsg::batch_send

streamer::sendmmsg::batch_send only requires an ExactSizeIterator:
https://github.com/anza-xyz/agave/blob/566bb9565/streamer/src/sendmmsg.rs#L203-L204
https://github.com/anza-xyz/agave/blob/566bb9565/streamer/src/sendmmsg.rs#L166-L175

Collecting an iterator into a vector before calling batch_send is
unnecessary and only adds overhead.
In particular multi_target_send used in retransmitting shreds can be use
without doing an additional vector allocation:
https://github.com/anza-xyz/agave/blob/566bb9565/streamer/src/sendmmsg.rs#L219

core/src/banking_stage/forwarder.rs

@@ -23,7 +23,6 @@ use {
     solana_sdk::{pubkey::Pubkey, transport::TransportError},
     solana_streamer::sendmmsg::batch_send,
     std::{
-        iter::repeat,
         net::{SocketAddr, UdpSocket},
         sync::{atomic::Ordering, Arc, RwLock},
     },
@@ -281,8 +280,8 @@ impl<T: LikeClusterInfo> Forwarder<T> {
         match forward_option {
             ForwardOption::ForwardTpuVote => {
                 // The vote must be forwarded using only UDP.
-                let pkts: Vec<_> = packet_vec.into_iter().zip(repeat(*addr)).collect();
-                batch_send(&self.socket, &pkts).map_err(|err| err.into())
+                let pkts = packet_vec.iter().map(|pkt| (pkt, addr));
+                batch_send(&self.socket, pkts).map_err(TransportError::from)
             }
             ForwardOption::ForwardTransaction => {
                 let conn = self.connection_cache.get_connection(addr);

core/src/forwarding_stage.rs

@@ -72,7 +72,8 @@ impl VoteClient {
     }
 
     fn send_batch(&self, batch: &mut Vec<(Vec<u8>, SocketAddr)>) {
-        let _res = batch_send(&self.udp_socket, batch);
+        let pkts = batch.iter().map(|(bytes, addr)| (bytes, addr));
+        let _res = batch_send(&self.udp_socket, pkts);
         batch.clear();
     }
 }

core/src/repair/repair_service.rs

@@ -646,15 +646,13 @@ impl RepairService {
 
             let mut batch_send_repairs_elapsed = Measure::start("batch_send_repairs_elapsed");
             if !batch.is_empty() {
-                match batch_send(repair_socket, &batch) {
+                let num_pkts = batch.len();
+                let batch = batch.iter().map(|(bytes, addr)| (bytes, addr));
+                match batch_send(repair_socket, batch) {
                     Ok(()) => (),
                     Err(SendPktsError::IoError(err, num_failed)) => {
                         error!(
-                            "{} batch_send failed to send {}/{} packets first error {:?}",
-                            id,
-                            num_failed,
-                            batch.len(),
-                            err
+                            "{id} batch_send failed to send {num_failed}/{num_pkts} packets first error {err:?}"
                         );
                     }
                 }
@@ -954,10 +952,10 @@ impl RepairService {
             ServeRepair::repair_proto_to_bytes(&request_proto, &identity_keypair).unwrap();
 
         // Prepare packet batch to send
-        let reqs = [(packet_buf, address)];
+        let reqs = [(&packet_buf, address)];
 
         // Send packet batch
-        match batch_send(repair_socket, &reqs[..]) {
+        match batch_send(repair_socket, reqs) {
             Ok(()) => {
                 debug!("successfully sent repair request to {pubkey} / {address}!");
             }

core/src/repair/serve_repair.rs

@@ -1249,14 +1249,13 @@ impl ServeRepair {
             }
         }
         if !pending_pongs.is_empty() {
-            match batch_send(repair_socket, &pending_pongs) {
+            let num_pkts = pending_pongs.len();
+            let pending_pongs = pending_pongs.iter().map(|(bytes, addr)| (bytes, addr));
+            match batch_send(repair_socket, pending_pongs) {
                 Ok(()) => (),
                 Err(SendPktsError::IoError(err, num_failed)) => {
                     warn!(
-                        "batch_send failed to send {}/{} packets. First error: {:?}",
-                        num_failed,
-                        pending_pongs.len(),
-                        err
+                        "batch_send failed to send {num_failed}/{num_pkts} packets. First error: {err:?}"
                     );
                 }
             }

streamer/src/sendmmsg.rs

@@ -16,7 +16,6 @@ use {
     std::{
         borrow::Borrow,
         io,
-        iter::repeat,
         net::{SocketAddr, UdpSocket},
     },
     thiserror::Error,
@@ -35,11 +34,15 @@ impl From<SendPktsError> for TransportError {
     }
 }
 
+// The type and lifetime constraints are overspecified to match 'linux' code.
 #[cfg(not(target_os = "linux"))]
-pub fn batch_send<S, T>(sock: &UdpSocket, packets: &[(T, S)]) -> Result<(), SendPktsError>
+pub fn batch_send<'a, S, T: 'a + ?Sized>(
+    sock: &UdpSocket,
+    packets: impl IntoIterator<Item = (&'a T, S), IntoIter: ExactSizeIterator>,
+) -> Result<(), SendPktsError>
 where
     S: Borrow<SocketAddr>,
-    T: AsRef<[u8]>,
+    &'a T: AsRef<[u8]>,
 {
     let mut num_failed = 0;
     let mut erropt = None;
@@ -158,11 +161,16 @@ fn sendmmsg_retry(sock: &UdpSocket, hdrs: &mut [mmsghdr]) -> Result<(), SendPkts
 const MAX_IOV: usize = libc::UIO_MAXIOV as usize;
 
 #[cfg(target_os = "linux")]
-pub fn batch_send_max_iov<S, T>(sock: &UdpSocket, packets: &[(T, S)]) -> Result<(), SendPktsError>
+pub fn batch_send_max_iov<'a, S, T: 'a + ?Sized>(
+    sock: &UdpSocket,
+    packets: impl IntoIterator<Item = (&'a T, S), IntoIter: ExactSizeIterator>,
+) -> Result<(), SendPktsError>
 where
     S: Borrow<SocketAddr>,
-    T: AsRef<[u8]>,
+    &'a T: AsRef<[u8]>,
 {
+    let packets = packets.into_iter();
+    let num_packets = packets.len();
     assert!(packets.len() <= MAX_IOV);
 
     let mut iovs = [MaybeUninit::uninit(); MAX_IOV];
@@ -177,13 +185,13 @@ where
     // SAFETY: The first `packets.len()` elements of `hdrs`, `iovs`, and `addrs` are
     // guaranteed to be initialized by `mmsghdr_for_packet` before this loop.
     let hdrs_slice =
-        unsafe { std::slice::from_raw_parts_mut(hdrs.as_mut_ptr() as *mut mmsghdr, packets.len()) };
+        unsafe { std::slice::from_raw_parts_mut(hdrs.as_mut_ptr() as *mut mmsghdr, num_packets) };
 
     let result = sendmmsg_retry(sock, hdrs_slice);
 
     // SAFETY: The first `packets.len()` elements of `hdrs`, `iovs`, and `addrs` are
     // guaranteed to be initialized by `mmsghdr_for_packet` before this loop.
-    for (hdr, iov, addr) in izip!(&mut hdrs, &mut iovs, &mut addrs).take(packets.len()) {
+    for (hdr, iov, addr) in izip!(&mut hdrs, &mut iovs, &mut addrs).take(num_packets) {
         unsafe {
             hdr.assume_init_drop();
             iov.assume_init_drop();
@@ -194,13 +202,23 @@ where
     result
 }
 
+// Need &'a to ensure that raw packet pointers obtained
+// in mmsghdr_for_packet stay valid.
 #[cfg(target_os = "linux")]
-pub fn batch_send<S, T>(sock: &UdpSocket, packets: &[(T, S)]) -> Result<(), SendPktsError>
+pub fn batch_send<'a, S, T: 'a + ?Sized>(
+    sock: &UdpSocket,
+    packets: impl IntoIterator<Item = (&'a T, S), IntoIter: ExactSizeIterator>,
+) -> Result<(), SendPktsError>
 where
     S: Borrow<SocketAddr>,
-    T: AsRef<[u8]>,
+    &'a T: AsRef<[u8]>,
 {
-    for chunk in packets.chunks(MAX_IOV) {
+    let mut packets = packets.into_iter();
+    loop {
+        let chunk = packets.by_ref().take(MAX_IOV);
+        if chunk.len() == 0 {
+            break;
+        }
         batch_send_max_iov(sock, chunk)?;
     }
     Ok(())
@@ -216,8 +234,8 @@ where
     T: AsRef<[u8]>,
 {
     let dests = dests.iter().map(Borrow::borrow);
-    let pkts: Vec<_> = repeat(&packet).zip(dests).collect();
-    batch_send(sock, &pkts)
+    let pkts = dests.map(|addr| (&packet, addr));
+    batch_send(sock, pkts)
 }
 
 #[cfg(test)]
@@ -246,7 +264,7 @@ mod tests {
         let packets: Vec<_> = (0..32).map(|_| vec![0u8; PACKET_DATA_SIZE]).collect();
         let packet_refs: Vec<_> = packets.iter().map(|p| (&p[..], &addr)).collect();
 
-        let sent = batch_send(&sender, &packet_refs[..]).ok();
+        let sent = batch_send(&sender, packet_refs).ok();
         assert_eq!(sent, Some(()));
 
         let mut packets = vec![Packet::default(); 32];
@@ -277,7 +295,7 @@ mod tests {
             })
             .collect();
 
-        let sent = batch_send(&sender, &packet_refs[..]).ok();
+        let sent = batch_send(&sender, packet_refs).ok();
         assert_eq!(sent, Some(()));
 
         let mut packets = vec![Packet::default(); 32];
@@ -345,7 +363,7 @@ mod tests {
         let dest_refs: Vec<_> = vec![&ip4, &ip6, &ip4];
 
         let sender = bind_to_unspecified().expect("bind");
-        let res = batch_send(&sender, &packet_refs[..]);
+        let res = batch_send(&sender, packet_refs);
         assert_matches!(res, Err(SendPktsError::IoError(_, /*num_failed*/ 1)));
         let res = multi_target_send(&sender, &packets[0], &dest_refs);
         assert_matches!(res, Err(SendPktsError::IoError(_, /*num_failed*/ 1)));
@@ -366,7 +384,7 @@ mod tests {
             (&packets[3][..], &ipv4broadcast),
             (&packets[4][..], &ipv4local),
         ];
-        match batch_send(&sender, &packet_refs[..]) {
+        match batch_send(&sender, packet_refs) {
             Ok(()) => panic!(),
             Err(SendPktsError::IoError(ioerror, num_failed)) => {
                 assert_matches!(ioerror.kind(), ErrorKind::PermissionDenied);
@@ -382,7 +400,7 @@ mod tests {
             (&packets[3][..], &ipv4local),
             (&packets[4][..], &ipv4broadcast),
         ];
-        match batch_send(&sender, &packet_refs[..]) {
+        match batch_send(&sender, packet_refs) {
             Ok(()) => panic!(),
             Err(SendPktsError::IoError(ioerror, num_failed)) => {
                 assert_matches!(ioerror.kind(), ErrorKind::PermissionDenied);
@@ -398,7 +416,7 @@ mod tests {
             (&packets[3][..], &ipv4broadcast),
             (&packets[4][..], &ipv4local),
         ];
-        match batch_send(&sender, &packet_refs[..]) {
+        match batch_send(&sender, packet_refs) {
             Ok(()) => panic!(),
             Err(SendPktsError::IoError(ioerror, num_failed)) => {
                 assert_matches!(ioerror.kind(), ErrorKind::PermissionDenied);

streamer/src/streamer.rs

@@ -362,7 +362,7 @@ fn recv_send(
         let data = pkt.data(..)?;
         socket_addr_space.check(&addr).then_some((data, addr))
     });
-    batch_send(sock, &packets.collect::<Vec<_>>())?;
+    batch_send(sock, packets.collect::<Vec<_>>())?;
     Ok(())
 }
 

turbine/src/broadcast_stage.rs

@@ -477,8 +477,9 @@ pub fn broadcast_shreds(
     shred_select.stop();
     transmit_stats.shred_select += shred_select.as_us();
 
+    let num_udp_packets = packets.len();
     let mut send_mmsg_time = Measure::start("send_mmsg");
-    match batch_send(s, &packets[..]) {
+    match batch_send(s, packets) {
         Ok(()) => (),
         Err(SendPktsError::IoError(ioerr, num_failed)) => {
             transmit_stats.dropped_packets_udp += num_failed;
@@ -487,7 +488,7 @@ pub fn broadcast_shreds(
     }
     send_mmsg_time.stop();
     transmit_stats.send_mmsg_elapsed += send_mmsg_time.as_us();
-    transmit_stats.total_packets += packets.len() + quic_packets.len();
+    transmit_stats.total_packets += num_udp_packets + quic_packets.len();
     for (shred, addr) in quic_packets {
         let shred = Bytes::from(shred::Payload::unwrap_or_clone(shred.clone()));
         if let Err(err) = quic_endpoint_sender.blocking_send((addr, shred)) {

turbine/src/broadcast_stage/broadcast_duplicates_run.rs

@@ -392,13 +392,7 @@ impl BroadcastRun for BroadcastDuplicatesRun {
             .flatten()
             .collect();
 
-        match batch_send(sock, &packets) {
-            Ok(()) => (),
-            Err(SendPktsError::IoError(ioerr, _)) => {
-                return Err(Error::Io(ioerr));
-            }
-        }
-        Ok(())
+        batch_send(sock, packets).map_err(|SendPktsError::IoError(err, _)| Error::Io(err))
     }
 
     fn record(&mut self, receiver: &RecordReceiver, blockstore: &Blockstore) -> Result<()> {

udp-client/src/udp_client.rs

@@ -2,7 +2,6 @@
 //! an interface for sending data
 
 use {
-    core::iter::repeat,
     solana_connection_cache::client_connection::ClientConnection,
     solana_streamer::sendmmsg::batch_send,
     solana_transaction_error::TransportResult,
@@ -37,18 +36,15 @@ impl ClientConnection for UdpClientConnection {
     }
 
     fn send_data_batch(&self, buffers: &[Vec<u8>]) -> TransportResult<()> {
-        let pkts: Vec<_> = buffers.iter().zip(repeat(self.server_addr())).collect();
-        batch_send(&self.socket, &pkts)?;
-        Ok(())
+        let addr = self.server_addr();
+        let pkts = buffers.iter().map(|bytes| (bytes, addr));
+        Ok(batch_send(&self.socket, pkts)?)
     }
 
     fn send_data_batch_async(&self, buffers: Vec<Vec<u8>>) -> TransportResult<()> {
-        let pkts: Vec<_> = buffers
-            .into_iter()
-            .zip(repeat(self.server_addr()))
-            .collect();
-        batch_send(&self.socket, &pkts)?;
-        Ok(())
+        let addr = self.server_addr();
+        let pkts = buffers.iter().map(|bytes| (bytes, addr));
+        Ok(batch_send(&self.socket, pkts)?)
     }
 
     fn send_data(&self, buffer: &[u8]) -> TransportResult<()> {