[fix-buffering] change request sending strategy and fix priorities

remove LAS, priorize new requests but otherwise just do standard queuing

src/net/message.rs

@@ -28,12 +28,30 @@ use crate::util::*;
 /// The same priority value is given to a request and to its associated response.
 pub type RequestPriority = u8;
 
+// Usage of priority levels in Garage:
+//
+// PRIO_HIGH
+//      for liveness check events such as pings and important
+//      reconfiguration events such as layout changes
+//
+// PRIO_NORMAL
+//      for standard interactive requests to exchange metadata
+//
+// PRIO_NORMAL | PRIO_SECONDARY
+//      for standard interactive requests to exchange block data
+//
+// PRIO_BACKGROUND
+//      for background resync requests to exchange metadata
+// PRIO_BACKGROUND | PRIO_SECONDARY
+//      for background resync requests to exchange block data
+
 /// Priority class: high
 pub const PRIO_HIGH: RequestPriority = 0x20;
 /// Priority class: normal
 pub const PRIO_NORMAL: RequestPriority = 0x40;
 /// Priority class: background
 pub const PRIO_BACKGROUND: RequestPriority = 0x80;
+
 /// Priority: primary among given class
 pub const PRIO_PRIMARY: RequestPriority = 0x00;
 /// Priority: secondary among given class (ex: `PRIO_HIGH | PRIO_SECONDARY`)

src/net/send.rs

@@ -109,7 +109,7 @@ impl SendQueuePriority {
 			let i = order_vec.iter().take_while(|o2| **o2 < order).count();
 			order_vec.insert(i, order);
 		}
-		self.items.push_front(item);
+		self.items.push_back(item);
 	}
 	fn remove(&mut self, id: RequestID) {
 		if let Some(i) = self.items.iter().position(|x| x.id == id) {
@@ -128,51 +128,56 @@ impl SendQueuePriority {
 		self.items.is_empty()
 	}
 	fn poll_next_ready(&mut self, ctx: &mut Context<'_>) -> Poll<(RequestID, DataFrame)> {
-		for (j, item) in self.items.iter_mut().enumerate() {
-			if let Some(OrderTag(stream, order)) = item.order_tag {
-				if order > *self.order.get(&stream).unwrap().front().unwrap() {
+		// in step 1: poll only streams that have sent 0 bytes, we want to send them in priority
+		//            as they most likely represent small requests to be sent first
+		// in step 2: poll all streams
+		for step in 0..2 {
+			for (j, item) in self.items.iter_mut().enumerate() {
+				if let Some(OrderTag(stream, order)) = item.order_tag {
+					if order > *self.order.get(&stream).unwrap().front().unwrap() {
+						continue;
+					}
+				}
+
+				if step == 0 && item.sent > 0 {
 					continue;
 				}
-			}
 
-			let mut item_reader = item.data.read_exact_or_eos(MAX_CHUNK_LENGTH as usize);
-			if let Poll::Ready(bytes_or_err) = Pin::new(&mut item_reader).poll(ctx) {
-				let id = item.id;
-				let eos = item.data.eos();
+				let mut item_reader = item.data.read_exact_or_eos(MAX_CHUNK_LENGTH as usize);
+				if let Poll::Ready(bytes_or_err) = Pin::new(&mut item_reader).poll(ctx) {
+					let id = item.id;
+					let eos = item.data.eos();
 
-				let packet = bytes_or_err.map_err(|e| match e {
-					ReadExactError::Stream(err) => err,
-					_ => unreachable!(),
-				});
+					let packet = bytes_or_err.map_err(|e| match e {
+						ReadExactError::Stream(err) => err,
+						_ => unreachable!(),
+					});
 
-				let is_err = packet.is_err();
-				let data_frame = DataFrame::from_packet(packet, !eos);
-				item.sent += data_frame.data().len();
+					let is_err = packet.is_err();
+					let data_frame = DataFrame::from_packet(packet, !eos);
+					item.sent += data_frame.data().len();
 
-				if eos || is_err {
-					// If item had an order tag, remove it from the corresponding ordering list
-					if let Some(OrderTag(stream, order)) = item.order_tag {
-						let order_stream = self.order.get_mut(&stream).unwrap();
-						assert_eq!(order_stream.pop_front(), Some(order));
-						if order_stream.is_empty() {
-							self.order.remove(&stream);
-						}
-					}
-					// Remove item from sending queue
-					self.items.remove(j);
-				} else {
-					// Move item later in send queue to implement LAS scheduling
-					// (LAS = Least Attained Service)
-					for k in j..self.items.len() - 1 {
-						if self.items[k].sent >= self.items[k + 1].sent {
-							self.items.swap(k, k + 1);
-						} else {
-							break;
+					if eos || is_err {
+						// If item had an order tag, remove it from the corresponding ordering list
+						if let Some(OrderTag(stream, order)) = item.order_tag {
+							let order_stream = self.order.get_mut(&stream).unwrap();
+							assert_eq!(order_stream.pop_front(), Some(order));
+							if order_stream.is_empty() {
+								self.order.remove(&stream);
+							}
 						}
+						// Remove item from sending queue
+						self.items.remove(j);
+					} else if step == 0 {
+						// Step 0 means that this stream had not sent any bytes yet.
+						// Now that it has, and it was not an EOS, we know that it is bigger
+						// than one chunk so move it at the end of the queue.
+						let item = self.items.remove(j).unwrap();
+						self.items.push_back(item);
 					}
+
+					return Poll::Ready((id, data_frame));
 				}
-
-				return Poll::Ready((id, data_frame));
 			}
 		}
 

src/net/server.rs

@@ -190,7 +190,7 @@ impl RecvLoop for ServerConn {
 
 			let (prio, resp_enc_result) = match ReqEnc::decode(stream).await {
 				Ok(req_enc) => (req_enc.prio, self2.recv_handler_aux(req_enc).await),
-				Err(e) => (PRIO_HIGH, Err(e)),
+				Err(e) => (PRIO_NORMAL, Err(e)),
 			};
 
 			debug!("server: sending response to {}", id);