refactor: only notify rx if there are processed packets

There is no point of notifing guest if there are no fully
processed packets.

Signed-off-by: Egor Lazarchuk <[email protected]>

Author: ShadowCurse

src/vmm/src/devices/virtio/net/device.rs

@@ -523,13 +523,16 @@ impl Net {
     }
 
     fn process_rx(&mut self) -> Result<(), DeviceError> {
+        let mut signal_queue = false;
         // Read as many frames as possible.
         loop {
             match self.read_from_mmds_or_tap() {
                 Ok(count) => {
                     self.rx_bytes_read = count;
                     self.metrics.rx_count.inc();
-                    if !self.rate_limited_rx_single_frame() {
+                    if self.rate_limited_rx_single_frame() {
+                        signal_queue = true;
+                    } else {
                         self.rx_deferred_frame = true;
                         break;
                     }
@@ -553,9 +556,12 @@ impl Net {
             }
         }
 
-        // At this point we processed as many Rx frames as possible.
-        // We have to wake the guest if at least one descriptor chain has been used.
-        self.signal_used_queue(NetQueue::Rx)
+        // We only notify guest if there is at least one packet processed successfully.
+        if signal_queue {
+            self.signal_used_queue(NetQueue::Rx)
+        } else {
+            Ok(())
+        }
     }
 
     // Process the deferred frame first, then continue reading from tap.