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* [PATCH] event/dsw: fix migration bug
@ 2022-07-07 11:43 Mattias Rönnblom
  2022-07-11 12:45 ` Jerin Jacob
  2022-09-13 12:53 ` Jerin Jacob
  0 siblings, 2 replies; 4+ messages in thread
From: Mattias Rönnblom @ 2022-07-07 11:43 UTC (permalink / raw)
  To: Jerin Jacob; +Cc: dev, Mattias Rönnblom, stable

From: Mattias Rönnblom <mattias.ronnblom@ericsson.com>

Fix bug in flow migration, which under certain conditions causes
reordering and violation of atomicity guarantees.

The issue occurs when the processing of a flow (on an atomic queue)
has resulted in events enqueued to a flow currently being migrated,
and the former (producer) flow is also selected for migration. The
events are buffered ("paused") on the originating port, and released
(forwarded) when the migration has completed. However, at the time of
"unpausing" the latter (consumer) flow, processing of the producer
flow on the port to which it was migrated may have already produced
events, for the same paused flow. This constitutes a race condition,
and depending on which port wins, reordering may have been introduced.

This patch forbids migration when a port has paused events, since
those events may have been the result of processing a to-be-migrated
flow.

This patch also disallows processing events pertaining to a flow under
migration, for the same reason. A new buffer is introduced, which
holds such not-yet-processed events dequeued from the port's input
ring. Such events are forwarded to the target port as a part of the
migration process.

The 'forwarding' migration state is eliminated, and instead background
processing is only performed if there are no unreleased events on the
port.

The bug is primarily triggered in situations where multiple flows are
migrated as one transaction, but may occur even if only a single flow
is migrated (e.g., with older DSW versions, which does not support
multi-flow migration).

Fixes: f6257b22e767 ("event/dsw: add load balancing")
Cc: stable@dpdk.org

Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
---
 drivers/event/dsw/dsw_evdev.h |   8 +-
 drivers/event/dsw/dsw_event.c | 315 ++++++++++++++++++++++++----------
 2 files changed, 232 insertions(+), 91 deletions(-)

diff --git a/drivers/event/dsw/dsw_evdev.h b/drivers/event/dsw/dsw_evdev.h
index c907c00c78..df7dcc5577 100644
--- a/drivers/event/dsw/dsw_evdev.h
+++ b/drivers/event/dsw/dsw_evdev.h
@@ -128,7 +128,6 @@ struct dsw_queue_flow {
 enum dsw_migration_state {
 	DSW_MIGRATION_STATE_IDLE,
 	DSW_MIGRATION_STATE_PAUSING,
-	DSW_MIGRATION_STATE_FORWARDING,
 	DSW_MIGRATION_STATE_UNPAUSING
 };
 
@@ -192,6 +191,13 @@ struct dsw_port {
 	uint16_t paused_events_len;
 	struct rte_event paused_events[DSW_MAX_EVENTS];
 
+	uint16_t emigrating_events_len;
+	/* Buffer for not-yet-processed events pertaining to a flow
+	 * emigrating from this port. These events will be forwarded
+	 * to the target port.
+	 */
+	struct rte_event emigrating_events[DSW_MAX_EVENTS];
+
 	uint16_t seen_events_len;
 	uint16_t seen_events_idx;
 	struct dsw_queue_flow seen_events[DSW_MAX_EVENTS_RECORDED];
diff --git a/drivers/event/dsw/dsw_event.c b/drivers/event/dsw/dsw_event.c
index e209cd5b00..c5fb0c8882 100644
--- a/drivers/event/dsw/dsw_event.c
+++ b/drivers/event/dsw/dsw_event.c
@@ -237,6 +237,15 @@ dsw_port_is_flow_paused(struct dsw_port *port, uint8_t queue_id,
 					queue_id, flow_hash);
 }
 
+static __rte_always_inline bool
+dsw_port_is_flow_migrating(struct dsw_port *port, uint8_t queue_id,
+			   uint16_t flow_hash)
+{
+	return dsw_is_queue_flow_in_ary(port->emigration_target_qfs,
+					port->emigration_targets_len,
+					queue_id, flow_hash);
+}
+
 static void
 dsw_port_add_paused_flows(struct dsw_port *port, struct dsw_queue_flow *qfs,
 			  uint8_t qfs_len)
@@ -271,9 +280,19 @@ dsw_port_remove_paused_flow(struct dsw_port *port,
 				port->paused_flows[i] =
 					port->paused_flows[last_idx];
 			port->paused_flows_len--;
-			break;
+
+			DSW_LOG_DP_PORT(DEBUG, port->id,
+					"Unpausing queue_id %d flow_hash %d.\n",
+					target_qf->queue_id,
+					target_qf->flow_hash);
+
+			return;
 		}
 	}
+
+	DSW_LOG_DP_PORT(ERR, port->id,
+			"Failed to unpause queue_id %d flow_hash %d.\n",
+			target_qf->queue_id, target_qf->flow_hash);
 }
 
 static void
@@ -284,7 +303,6 @@ dsw_port_remove_paused_flows(struct dsw_port *port,
 
 	for (i = 0; i < qfs_len; i++)
 		dsw_port_remove_paused_flow(port, &qfs[i]);
-
 }
 
 static void
@@ -439,14 +457,15 @@ dsw_is_serving_port(struct dsw_evdev *dsw, uint8_t port_id, uint8_t queue_id)
 
 static bool
 dsw_select_emigration_target(struct dsw_evdev *dsw,
-			    struct dsw_queue_flow_burst *bursts,
-			    uint16_t num_bursts, uint8_t source_port_id,
-			    int16_t *port_loads, uint16_t num_ports,
-			    uint8_t *target_port_ids,
-			    struct dsw_queue_flow *target_qfs,
-			    uint8_t *targets_len)
-{
-	int16_t source_port_load = port_loads[source_port_id];
+			     struct dsw_port *source_port,
+			     struct dsw_queue_flow_burst *bursts,
+			     uint16_t num_bursts,
+			     int16_t *port_loads, uint16_t num_ports,
+			     uint8_t *target_port_ids,
+			     struct dsw_queue_flow *target_qfs,
+			     uint8_t *targets_len)
+{
+	int16_t source_port_load = port_loads[source_port->id];
 	struct dsw_queue_flow *candidate_qf = NULL;
 	uint8_t candidate_port_id = 0;
 	int16_t candidate_weight = -1;
@@ -471,7 +490,7 @@ dsw_select_emigration_target(struct dsw_evdev *dsw,
 		for (port_id = 0; port_id < num_ports; port_id++) {
 			int16_t weight;
 
-			if (port_id == source_port_id)
+			if (port_id == source_port->id)
 				continue;
 
 			if (!dsw_is_serving_port(dsw, port_id, qf->queue_id))
@@ -493,7 +512,7 @@ dsw_select_emigration_target(struct dsw_evdev *dsw,
 	if (candidate_weight < 0)
 		return false;
 
-	DSW_LOG_DP_PORT(DEBUG, source_port_id, "Selected queue_id %d "
+	DSW_LOG_DP_PORT(DEBUG, source_port->id, "Selected queue_id %d "
 			"flow_hash %d (with flow load %d) for migration "
 			"to port %d.\n", candidate_qf->queue_id,
 			candidate_qf->flow_hash,
@@ -501,7 +520,7 @@ dsw_select_emigration_target(struct dsw_evdev *dsw,
 			candidate_port_id);
 
 	port_loads[candidate_port_id] += candidate_flow_load;
-	port_loads[source_port_id] -= candidate_flow_load;
+	port_loads[source_port->id] -= candidate_flow_load;
 
 	target_port_ids[*targets_len] = candidate_port_id;
 	target_qfs[*targets_len] = *candidate_qf;
@@ -527,8 +546,8 @@ dsw_select_emigration_targets(struct dsw_evdev *dsw,
 	for (i = 0; i < DSW_MAX_FLOWS_PER_MIGRATION; i++) {
 		bool found;
 
-		found = dsw_select_emigration_target(dsw, bursts, num_bursts,
-						     source_port->id,
+		found = dsw_select_emigration_target(dsw, source_port,
+						     bursts, num_bursts,
 						     port_loads, dsw->num_ports,
 						     target_port_ids,
 						     target_qfs,
@@ -608,6 +627,7 @@ dsw_port_buffer_paused(struct dsw_port *port,
 	port->paused_events_len++;
 }
 
+
 static void
 dsw_port_buffer_non_paused(struct dsw_evdev *dsw, struct dsw_port *source_port,
 			   uint8_t dest_port_id, const struct rte_event *event)
@@ -679,40 +699,39 @@ dsw_port_buffer_event(struct dsw_evdev *dsw, struct dsw_port *source_port,
 }
 
 static void
-dsw_port_flush_paused_events(struct dsw_evdev *dsw,
-			     struct dsw_port *source_port,
-			     const struct dsw_queue_flow *qf)
+dsw_port_flush_no_longer_paused_events(struct dsw_evdev *dsw,
+				       struct dsw_port *source_port)
 {
 	uint16_t paused_events_len = source_port->paused_events_len;
 	struct rte_event paused_events[paused_events_len];
-	uint8_t dest_port_id;
 	uint16_t i;
 
 	if (paused_events_len == 0)
 		return;
 
-	if (dsw_port_is_flow_paused(source_port, qf->queue_id, qf->flow_hash))
-		return;
-
 	rte_memcpy(paused_events, source_port->paused_events,
 		   paused_events_len * sizeof(struct rte_event));
 
 	source_port->paused_events_len = 0;
 
-	dest_port_id = dsw_schedule(dsw, qf->queue_id, qf->flow_hash);
-
 	for (i = 0; i < paused_events_len; i++) {
 		struct rte_event *event = &paused_events[i];
 		uint16_t flow_hash;
 
 		flow_hash = dsw_flow_id_hash(event->flow_id);
 
-		if (event->queue_id == qf->queue_id &&
-		    flow_hash == qf->flow_hash)
+		if (dsw_port_is_flow_paused(source_port, event->queue_id,
+					    flow_hash))
+			dsw_port_buffer_paused(source_port, event);
+		else {
+			uint8_t dest_port_id;
+
+			dest_port_id = dsw_schedule(dsw, event->queue_id,
+						    flow_hash);
+
 			dsw_port_buffer_non_paused(dsw, source_port,
 						   dest_port_id, event);
-		else
-			dsw_port_buffer_paused(source_port, event);
+		}
 	}
 }
 
@@ -755,11 +774,6 @@ dsw_port_end_emigration(struct dsw_evdev *dsw, struct dsw_port *port,
 		DSW_LOG_DP_PORT(DEBUG, port->id, "Migration completed for "
 				"queue_id %d flow_hash %d.\n", queue_id,
 				flow_hash);
-
-		if (queue_schedule_type == RTE_SCHED_TYPE_ATOMIC) {
-			dsw_port_remove_paused_flow(port, qf);
-			dsw_port_flush_paused_events(dsw, port, qf);
-		}
 	}
 
 	finished = port->emigration_targets_len - left_qfs_len;
@@ -826,10 +840,31 @@ dsw_port_consider_emigration(struct dsw_evdev *dsw,
 	if (dsw->num_ports == 1)
 		return;
 
-	if (seen_events_len < DSW_MAX_EVENTS_RECORDED)
+	DSW_LOG_DP_PORT(DEBUG, source_port->id, "Considering emigration.\n");
+
+	if (seen_events_len < DSW_MAX_EVENTS_RECORDED) {
+		DSW_LOG_DP_PORT(DEBUG, source_port->id, "Not enough events "
+				"are recorded to allow for a migration.\n");
 		return;
+	}
 
-	DSW_LOG_DP_PORT(DEBUG, source_port->id, "Considering emigration.\n");
+	/* A flow migration cannot be initiated if there are paused
+	 * events, since some/all of those events may be have been
+	 * produced as a result of processing the flow(s) selected for
+	 * migration. Moving such a flow would potentially introduced
+	 * reordering, since processing the migrated flow on the
+	 * receiving flow may commence before the to-be-enqueued-to
+
+	 * flows are unpaused, leading to paused events on the second
+	 * port as well, destined for the same paused flow(s). When
+	 * those flows are unpaused, the resulting events are
+	 * delivered the owning port in an undefined order.
+	 */
+	if (source_port->paused_events_len > 0) {
+		DSW_LOG_DP_PORT(DEBUG, source_port->id, "There are "
+				"events in the paus buffer.\n");
+		return;
+	}
 
 	/* Randomize interval to avoid having all threads considering
 	 * emigration at the same in point in time, which might lead
@@ -927,9 +962,8 @@ dsw_port_consider_emigration(struct dsw_evdev *dsw,
 }
 
 static void
-dsw_port_flush_paused_events(struct dsw_evdev *dsw,
-			     struct dsw_port *source_port,
-			     const struct dsw_queue_flow *qf);
+dsw_port_flush_no_longer_paused_events(struct dsw_evdev *dsw,
+				       struct dsw_port *source_port);
 
 static void
 dsw_port_handle_unpause_flows(struct dsw_evdev *dsw, struct dsw_port *port,
@@ -954,62 +988,123 @@ dsw_port_handle_unpause_flows(struct dsw_evdev *dsw, struct dsw_port *port,
 
 		if (dsw_schedule(dsw, qf->queue_id, qf->flow_hash) == port->id)
 			port->immigrations++;
+	}
+
+	dsw_port_flush_no_longer_paused_events(dsw, port);
+}
+
+static void
+dsw_port_buffer_in_buffer(struct dsw_port *port,
+			  const struct rte_event *event)
+
+{
+	RTE_ASSERT(port->in_buffer_start == 0);
+
+	port->in_buffer[port->in_buffer_len] = *event;
+	port->in_buffer_len++;
+}
+
+static void
+dsw_port_forward_emigrated_event(struct dsw_evdev *dsw,
+				 struct dsw_port *source_port,
+				 struct rte_event *event)
+{
+	uint16_t i;
+
+	for (i = 0; i < source_port->emigration_targets_len; i++) {
+		struct dsw_queue_flow *qf =
+			&source_port->emigration_target_qfs[i];
+		uint8_t dest_port_id =
+			source_port->emigration_target_port_ids[i];
+		struct dsw_port *dest_port = &dsw->ports[dest_port_id];
 
-		dsw_port_flush_paused_events(dsw, port, qf);
+		if (event->queue_id == qf->queue_id &&
+		    dsw_flow_id_hash(event->flow_id) == qf->flow_hash) {
+			/* No need to care about bursting forwarded
+			 * events (to the destination port's in_ring),
+			 * since migration doesn't happen very often,
+			 * and also the majority of the dequeued
+			 * events will likely *not* be forwarded.
+			 */
+			while (rte_event_ring_enqueue_burst(dest_port->in_ring,
+							    event, 1,
+							    NULL) != 1)
+				rte_pause();
+			return;
+		}
 	}
+
+	/* Event did not belong to the emigrated flows */
+	dsw_port_buffer_in_buffer(source_port, event);
 }
 
-#define FORWARD_BURST_SIZE (32)
+static void
+dsw_port_stash_migrating_event(struct dsw_port *port,
+			       const struct rte_event *event)
+{
+	port->emigrating_events[port->emigrating_events_len] = *event;
+	port->emigrating_events_len++;
+}
+
+#define DRAIN_DEQUEUE_BURST_SIZE (32)
 
 static void
-dsw_port_forward_emigrated_flow(struct dsw_port *source_port,
-				struct rte_event_ring *dest_ring,
-				uint8_t queue_id,
-				uint16_t flow_hash)
+dsw_port_drain_in_ring(struct dsw_port *source_port)
 {
-	uint16_t events_left;
+	uint16_t num_events;
+	uint16_t dequeued;
 
 	/* Control ring message should been seen before the ring count
 	 * is read on the port's in_ring.
 	 */
 	rte_smp_rmb();
 
-	events_left = rte_event_ring_count(source_port->in_ring);
+	num_events = rte_event_ring_count(source_port->in_ring);
 
-	while (events_left > 0) {
-		uint16_t in_burst_size =
-			RTE_MIN(FORWARD_BURST_SIZE, events_left);
-		struct rte_event in_burst[in_burst_size];
-		uint16_t in_len;
+	for (dequeued = 0; dequeued < num_events; ) {
+		uint16_t burst_size = RTE_MIN(DRAIN_DEQUEUE_BURST_SIZE,
+					      num_events - dequeued);
+		struct rte_event events[burst_size];
+		uint16_t len;
 		uint16_t i;
 
-		in_len = rte_event_ring_dequeue_burst(source_port->in_ring,
-						      in_burst,
-						      in_burst_size, NULL);
-		/* No need to care about bursting forwarded events (to
-		 * the destination port's in_ring), since migration
-		 * doesn't happen very often, and also the majority of
-		 * the dequeued events will likely *not* be forwarded.
-		 */
-		for (i = 0; i < in_len; i++) {
-			struct rte_event *e = &in_burst[i];
-			if (e->queue_id == queue_id &&
-			    dsw_flow_id_hash(e->flow_id) == flow_hash) {
-				while (rte_event_ring_enqueue_burst(dest_ring,
-								    e, 1,
-								    NULL) != 1)
-					rte_pause();
-			} else {
-				uint16_t last_idx = source_port->in_buffer_len;
-				source_port->in_buffer[last_idx] = *e;
-				source_port->in_buffer_len++;
-			}
+		len = rte_event_ring_dequeue_burst(source_port->in_ring,
+						   events, burst_size,
+						   NULL);
+
+		for (i = 0; i < len; i++) {
+			struct rte_event *event = &events[i];
+			uint16_t flow_hash;
+
+			flow_hash = dsw_flow_id_hash(event->flow_id);
+
+			if (unlikely(dsw_port_is_flow_migrating(source_port,
+								event->queue_id,
+								flow_hash)))
+				dsw_port_stash_migrating_event(source_port,
+							       event);
+			else
+				dsw_port_buffer_in_buffer(source_port, event);
 		}
 
-		events_left -= in_len;
+		dequeued += len;
 	}
 }
 
+static void
+dsw_port_forward_emigrated_flows(struct dsw_evdev *dsw,
+				 struct dsw_port *source_port)
+{
+	uint16_t i;
+
+	for (i = 0; i < source_port->emigrating_events_len; i++) {
+		struct rte_event *event = &source_port->emigrating_events[i];
+
+		dsw_port_forward_emigrated_event(dsw, source_port, event);
+	}
+	source_port->emigrating_events_len = 0;
+}
+
 static void
 dsw_port_move_emigrating_flows(struct dsw_evdev *dsw,
 			       struct dsw_port *source_port)
@@ -1018,22 +1113,27 @@ dsw_port_move_emigrating_flows(struct dsw_evdev *dsw,
 
 	dsw_port_flush_out_buffers(dsw, source_port);
 
-	rte_smp_wmb();
-
 	for (i = 0; i < source_port->emigration_targets_len; i++) {
 		struct dsw_queue_flow *qf =
 			&source_port->emigration_target_qfs[i];
 		uint8_t dest_port_id =
 			source_port->emigration_target_port_ids[i];
-		struct dsw_port *dest_port = &dsw->ports[dest_port_id];
 
 		dsw->queues[qf->queue_id].flow_to_port_map[qf->flow_hash] =
-			dest_port_id;
-
-		dsw_port_forward_emigrated_flow(source_port, dest_port->in_ring,
-						qf->queue_id, qf->flow_hash);
+		    dest_port_id;
 	}
 
+	rte_smp_wmb();
+
+	dsw_port_drain_in_ring(source_port);
+	dsw_port_forward_emigrated_flows(dsw, source_port);
+
+	dsw_port_remove_paused_flows(source_port,
+				     source_port->emigration_target_qfs,
+				     source_port->emigration_targets_len);
+
+	dsw_port_flush_no_longer_paused_events(dsw, source_port);
+
 	/* Flow table update and migration destination port's enqueues
 	 * must be seen before the control message.
 	 */
@@ -1054,9 +1154,7 @@ dsw_port_handle_confirm(struct dsw_evdev *dsw, struct dsw_port *port)
 	if (port->cfm_cnt == (dsw->num_ports-1)) {
 		switch (port->migration_state) {
 		case DSW_MIGRATION_STATE_PAUSING:
-			DSW_LOG_DP_PORT(DEBUG, port->id, "Going into forwarding "
-					"migration state.\n");
-			port->migration_state = DSW_MIGRATION_STATE_FORWARDING;
+			dsw_port_move_emigrating_flows(dsw, port);
 			break;
 		case DSW_MIGRATION_STATE_UNPAUSING:
 			dsw_port_end_emigration(dsw, port,
@@ -1096,18 +1194,18 @@ dsw_port_ctl_process(struct dsw_evdev *dsw, struct dsw_port *port)
 static void
 dsw_port_note_op(struct dsw_port *port, uint16_t num_events)
 {
-	/* To pull the control ring reasonably often on busy ports,
-	 * each dequeued/enqueued event is considered an 'op' too.
-	 */
 	port->ops_since_bg_task += (num_events+1);
 }
 
 static void
 dsw_port_bg_process(struct dsw_evdev *dsw, struct dsw_port *port)
 {
-	if (unlikely(port->migration_state == DSW_MIGRATION_STATE_FORWARDING &&
-		     port->pending_releases == 0))
-		dsw_port_move_emigrating_flows(dsw, port);
+	/* For simplicity (in the migration logic), avoid all
+	 * background processing in case event processing is in
+	 * progress.
+	 */
+	if (port->pending_releases > 0)
+		return;
 
 	/* Polling the control ring is relatively inexpensive, and
 	 * polling it often helps bringing down migration latency, so
@@ -1167,7 +1265,7 @@ dsw_event_enqueue_burst_generic(struct dsw_port *source_port,
 	uint16_t i;
 
 	DSW_LOG_DP_PORT(DEBUG, source_port->id, "Attempting to enqueue %d "
-			"events to port %d.\n", events_len, source_port->id);
+			"events.\n", events_len);
 
 	dsw_port_bg_process(dsw, source_port);
 
@@ -1351,6 +1449,38 @@ dsw_port_dequeue_burst(struct dsw_port *port, struct rte_event *events,
 	return rte_event_ring_dequeue_burst(port->in_ring, events, num, NULL);
 }
 
+static void
+dsw_port_stash_migrating_events(struct dsw_port *port,
+				struct rte_event *events, uint16_t *num)
+{
+	uint16_t i;
+
+	/* The assumption here - performance-wise - is that events
+	 * belonging to migrating flows are relatively rare.
+	 */
+	for (i = 0; i < (*num); ) {
+		struct rte_event *event = &events[i];
+		uint16_t flow_hash;
+
+		flow_hash = dsw_flow_id_hash(event->flow_id);
+
+		if (unlikely(dsw_port_is_flow_migrating(port, event->queue_id,
+							flow_hash))) {
+			uint16_t left;
+
+			dsw_port_stash_migrating_event(port, event);
+
+			(*num)--;
+			left = *num - i;
+
+			if (left > 0)
+				memmove(event, event + 1,
+					left * sizeof(struct rte_event));
+		} else
+			i++;
+	}
+}
+
 uint16_t
 dsw_event_dequeue_burst(void *port, struct rte_event *events, uint16_t num,
 			uint64_t wait __rte_unused)
@@ -1368,6 +1498,11 @@ dsw_event_dequeue_burst(void *port, struct rte_event *events, uint16_t num,
 
 	dequeued = dsw_port_dequeue_burst(source_port, events, num);
 
+	if (unlikely(source_port->migration_state ==
+		     DSW_MIGRATION_STATE_PAUSING))
+		dsw_port_stash_migrating_events(source_port, events,
+						&dequeued);
+
 	source_port->pending_releases = dequeued;
 
 	dsw_port_load_record(source_port, dequeued);
-- 
2.25.1


^ permalink raw reply	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-09-13 12:53 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2022-07-07 11:43 [PATCH] event/dsw: fix migration bug Mattias Rönnblom
2022-07-11 12:45 ` Jerin Jacob
2022-07-11 20:43   ` Thomas Monjalon
2022-09-13 12:53 ` Jerin Jacob

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