vsock: Move iter outside of loop in process_rx_queue

the iter() function is used for produce a queue iterator to iterate over
the descriptors.

But usually, it shouldn't be in the while loop, which might brings more
unnecessary overhead.

So move `iter` outside of the while loop.

And the process_tx_queue has the same problem, maybe we can fix it, too.

Signed-off-by: Li Zebin <cutelizebin@gmail.com>

Author: cutelizebin

crates/vsock/src/vhu_vsock_thread.rs

@@ -462,76 +462,81 @@ impl VhostUserVsockThread {
 
         let queue = vring_mut.get_queue_mut();
 
-        while let Some(mut avail_desc) = queue
-            .iter(atomic_mem.memory())
-            .map_err(|_| Error::IterateQueue)?
-            .next()
-        {
-            used_any = true;
-            let mem = atomic_mem.clone().memory();
-
-            let head_idx = avail_desc.head_index();
-            let used_len = match VsockPacket::from_rx_virtq_chain(
-                mem.deref(),
-                &mut avail_desc,
-                self.tx_buffer_size,
-            ) {
-                Ok(mut pkt) => {
-                    let recv_result = match rx_queue_type {
-                        RxQueueType::Standard => self.thread_backend.recv_pkt(&mut pkt),
-                        RxQueueType::RawPkts => self.thread_backend.recv_raw_pkt(&mut pkt),
-                    };
-
-                    if recv_result.is_ok() {
-                        PKT_HEADER_SIZE + pkt.len() as usize
-                    } else {
-                        queue.iter(mem).unwrap().go_to_previous_position();
-                        break;
+        let mut iter_has_elemnt = true;
+        while iter_has_elemnt {
+            let queue_iter = queue
+                .iter(atomic_mem.memory())
+                .map_err(|_| Error::IterateQueue)?;
+
+            iter_has_elemnt = false;
+            for mut avail_desc in queue_iter {
+                used_any = true;
+                iter_has_elemnt = true;
+                let mem = atomic_mem.clone().memory();
+
+                let head_idx = avail_desc.head_index();
+                let used_len = match VsockPacket::from_rx_virtq_chain(
+                    mem.deref(),
+                    &mut avail_desc,
+                    self.tx_buffer_size,
+                ) {
+                    Ok(mut pkt) => {
+                        let recv_result = match rx_queue_type {
+                            RxQueueType::Standard => self.thread_backend.recv_pkt(&mut pkt),
+                            RxQueueType::RawPkts => self.thread_backend.recv_raw_pkt(&mut pkt),
+                        };
+
+                        if recv_result.is_ok() {
+                            PKT_HEADER_SIZE + pkt.len() as usize
+                        } else {
+                            queue.iter(mem).unwrap().go_to_previous_position();
+                            break;
+                        }
                     }
-                }
-                Err(e) => {
-                    warn!("vsock: RX queue error: {:?}", e);
-                    0
-                }
-            };
+                    Err(e) => {
+                        warn!("vsock: RX queue error: {:?}", e);
+                        0
+                    }
+                };
 
-            let vring = vring.clone();
-            let event_idx = self.event_idx;
+                let vring = vring.clone();
+                let event_idx = self.event_idx;
 
-            self.pool.spawn_ok(async move {
-                // TODO: Understand why doing the following in the pool works
-                if event_idx {
-                    if vring.add_used(head_idx, used_len as u32).is_err() {
-                        warn!("Could not return used descriptors to ring");
-                    }
-                    match vring.needs_notification() {
-                        Err(_) => {
-                            warn!("Could not check if queue needs to be notified");
-                            vring.signal_used_queue().unwrap();
+                self.pool.spawn_ok(async move {
+                    // TODO: Understand why doing the following in the pool works
+                    if event_idx {
+                        if vring.add_used(head_idx, used_len as u32).is_err() {
+                            warn!("Could not return used descriptors to ring");
                         }
-                        Ok(needs_notification) => {
-                            if needs_notification {
+                        match vring.needs_notification() {
+                            Err(_) => {
+                                warn!("Could not check if queue needs to be notified");
                                 vring.signal_used_queue().unwrap();
                             }
+                            Ok(needs_notification) => {
+                                if needs_notification {
+                                    vring.signal_used_queue().unwrap();
+                                }
+                            }
                         }
+                    } else {
+                        if vring.add_used(head_idx, used_len as u32).is_err() {
+                            warn!("Could not return used descriptors to ring");
+                        }
+                        vring.signal_used_queue().unwrap();
                     }
-                } else {
-                    if vring.add_used(head_idx, used_len as u32).is_err() {
-                        warn!("Could not return used descriptors to ring");
-                    }
-                    vring.signal_used_queue().unwrap();
-                }
-            });
+                });
 
-            match rx_queue_type {
-                RxQueueType::Standard => {
-                    if !self.thread_backend.pending_rx() {
-                        break;
+                match rx_queue_type {
+                    RxQueueType::Standard => {
+                        if !self.thread_backend.pending_rx() {
+                            break;
+                        }
                     }
-                }
-                RxQueueType::RawPkts => {
-                    if !self.thread_backend.pending_raw_pkts() {
-                        break;
+                    RxQueueType::RawPkts => {
+                        if !self.thread_backend.pending_raw_pkts() {
+                            break;
+                        }
                     }
                 }
             }