perf(executor): Catch up on network work before returning

When the point in time that smoltcp thinks the interface should be
polled again is in the past, we should try to poll it immediately to
avoid lagging behind.

Signed-off-by: Jens Reidel <[email protected]>

Author: Gelbpunkt

src/executor/mod.rs

@@ -143,6 +143,36 @@ where
 	}
 }
 
+fn maybe_set_network_timer(now: u64) {
+	if let Some(mut guard) = crate::executor::network::NIC.try_lock() {
+		let delay = if let Ok(nic) = guard.as_nic_mut() {
+			let mut delay_micros = nic
+				.poll_delay(Instant::from_micros_const(now.try_into().unwrap()))
+				.map(|d| d.total_micros());
+
+			// Under heavy workloads, we may be lagging behind, in which case we
+			// need to try to catch up immediately
+			while delay_micros == Some(0) {
+				nic.poll_common(crate::executor::network::now());
+				delay_micros = nic
+					.poll_delay(crate::executor::network::now())
+					.map(|d| d.total_micros());
+			}
+
+			// We will yield back to userspace and may not have an opportunity to handle
+			// network traffic unless we enable interrupts
+			nic.set_polling_mode(false);
+
+			delay_micros
+		} else {
+			None
+		};
+
+		core_local::core_scheduler()
+			.add_network_timer(delay.map(|d| crate::arch::processor::get_timer_ticks() + d));
+	}
+}
+
 /// Blocks the current thread on `f`, running the executor when idling.
 pub(crate) fn block_on<F, T>(future: F, timeout: Option<Duration>) -> io::Result<T>
 where
@@ -166,21 +196,7 @@ where
 		if let Poll::Ready(t) = result {
 			// allow network interrupts
 			#[cfg(feature = "net")]
-			{
-				if let Some(mut guard) = crate::executor::network::NIC.try_lock() {
-					let delay = if let Ok(nic) = guard.as_nic_mut() {
-						nic.set_polling_mode(false);
-
-						nic.poll_delay(Instant::from_micros_const(now.try_into().unwrap()))
-							.map(|d| d.total_micros())
-					} else {
-						None
-					};
-					core_local::core_scheduler().add_network_timer(
-						delay.map(|d| crate::arch::processor::get_timer_ticks() + d),
-					);
-				}
-			}
+			maybe_set_network_timer(now);
 
 			return t;
 		}
@@ -190,21 +206,7 @@ where
 		{
 			// allow network interrupts
 			#[cfg(feature = "net")]
-			{
-				if let Some(mut guard) = crate::executor::network::NIC.try_lock() {
-					let delay = if let Ok(nic) = guard.as_nic_mut() {
-						nic.set_polling_mode(false);
-
-						nic.poll_delay(Instant::from_micros_const(now.try_into().unwrap()))
-							.map(|d| d.total_micros())
-					} else {
-						None
-					};
-					core_local::core_scheduler().add_network_timer(
-						delay.map(|d| crate::arch::processor::get_timer_ticks() + d),
-					);
-				}
-			}
+			maybe_set_network_timer(now);
 
 			return Err(Errno::Time);
 		}