Raise interrupt for used descriptors on tx queue.

Add a unit test for this regression: #1436.

Signed-off-by: Andrei Sandu <[email protected]>

Author: sandreim

CHANGELOG.md

@@ -8,6 +8,9 @@
 - The backtrace are printed on `panic`, no longer causing a seccomp fault.
 - Fixed #1375 - Change logger options type from Value to Vec<LogOption> to
   prevent potential unwrap on None panics.
+- Raise interrupt for TX queue used descriptors - Github issue #1436
+- Fixed a bug that causes 100% cpu load when the net device rx is throttled 
+  by the ratelimiter - Github issue #1439
 
 ## [0.19.0]
 

src/devices/src/virtio/net.rs

@@ -397,6 +397,7 @@ impl NetEpollHandler {
         // trigger a process_rx() which checks if there are any new frames to be sent, starting
         // with the MMDS network stack.
         let mut process_rx_for_mmds = false;
+        let mut raise_irq = false;
 
         while let Some(head) = self.tx.queue.pop(&self.mem) {
             // If limiter.consume() fails it means there is no more TokenType::Ops
@@ -474,6 +475,11 @@ impl NetEpollHandler {
             }
 
             self.tx.queue.add_used(&self.mem, head_index, 0);
+            raise_irq = true;
+        }
+        
+        if raise_irq {
+            self.signal_used_queue()?;
         }
 
         // An incoming frame for the MMDS may trigger the transmission of a new message.
@@ -1599,7 +1605,7 @@ mod tests {
             h.interrupt_evt.write(1).unwrap();
             h.handle_event(RX_TAP_EVENT, EPOLLIN).unwrap();
             assert!(h.rx.deferred_frame);
-            assert_eq!(h.interrupt_evt.read().unwrap(), 2);
+            assert_eq!(h.interrupt_evt.read().unwrap(), 3);
             // The #cfg(test) enabled version of read_tap always returns 1234 bytes (or the len of
             // the buffer, whichever is smaller).
             assert_eq!(rxq.used.ring[0].get().len, 1234);
@@ -1750,7 +1756,7 @@ mod tests {
                 assert!(h.get_rx_rate_limiter().is_blocked());
                 assert!(h.rx.deferred_frame);
                 // assert that no operation actually completed (limiter blocked it)
-                assert_eq!(h.interrupt_evt.read().unwrap(), 1);
+                assert_eq!(h.interrupt_evt.read().unwrap(), 2);
                 // make sure the data is still queued for processing
                 assert_eq!(rxq.used.idx.get(), 0);
             }
@@ -1853,7 +1859,7 @@ mod tests {
                 assert!(h.get_rx_rate_limiter().is_blocked());
                 assert!(h.rx.deferred_frame);
                 // assert that no operation actually completed (limiter blocked it)
-                assert_eq!(h.interrupt_evt.read().unwrap(), 1);
+                assert_eq!(h.interrupt_evt.read().unwrap(), 2);
                 // make sure the data is still queued for processing
                 assert_eq!(rxq.used.idx.get(), 0);