[PATCH] Improve the shaper accuracy for large packets

[alanrobertsonatt@gmail.com]

From: Alan Robertson <ar771e@att.com>

There were 2 issues, the first was time could be lost whilst updating
the traffic-class period, the second was a frame could be delayed if
not enough tokens were available for the full frame.  By allowing the
shaper to borrow credit from the next period the throughput is improved.
---
 lib/librte_sched/rte_sched.c | 58 +++++++++++++++++++++++++++++++-------------
 1 file changed, 41 insertions(+), 17 deletions(-)

diff --git a/lib/librte_sched/rte_sched.c b/lib/librte_sched/rte_sched.c
index 634486c..e53a424 100644
--- a/lib/librte_sched/rte_sched.c
+++ b/lib/librte_sched/rte_sched.c
@@ -57,7 +57,7 @@ struct rte_sched_subport {
 	/* Traffic classes (TCs) */
 	uint64_t tc_time; /* time of next update */
 	uint32_t tc_credits_per_period[RTE_SCHED_TRAFFIC_CLASSES_PER_PIPE];
-	uint32_t tc_credits[RTE_SCHED_TRAFFIC_CLASSES_PER_PIPE];
+	int32_t tc_credits[RTE_SCHED_TRAFFIC_CLASSES_PER_PIPE];
 	uint32_t tc_period;
 
 	/* TC oversubscription */
@@ -98,7 +98,7 @@ struct rte_sched_pipe {
 
 	/* Traffic classes (TCs) */
 	uint64_t tc_time; /* time of next update */
-	uint32_t tc_credits[RTE_SCHED_TRAFFIC_CLASSES_PER_PIPE];
+	int32_t tc_credits[RTE_SCHED_TRAFFIC_CLASSES_PER_PIPE];
 
 	/* Weighted Round Robin (WRR) */
 	uint8_t wrr_tokens[RTE_SCHED_QUEUES_PER_PIPE];
@@ -1451,6 +1451,8 @@ grinder_credits_update(struct rte_sched_port *port, uint32_t pos)
 	struct rte_sched_pipe *pipe = grinder->pipe;
 	struct rte_sched_pipe_profile *params = grinder->pipe_params;
 	uint64_t n_periods;
+	uint32_t tc;
+	uint64_t lapsed;
 
 	/* Subport TB */
 	n_periods = (port->time - subport->tb_time) / subport->tb_period;
@@ -1466,20 +1468,42 @@ grinder_credits_update(struct rte_sched_port *port, uint32_t pos)
 
 	/* Subport TCs */
 	if (unlikely(port->time >= subport->tc_time)) {
-		subport->tc_credits[0] = subport->tc_credits_per_period[0];
-		subport->tc_credits[1] = subport->tc_credits_per_period[1];
-		subport->tc_credits[2] = subport->tc_credits_per_period[2];
-		subport->tc_credits[3] = subport->tc_credits_per_period[3];
-		subport->tc_time = port->time + subport->tc_period;
+		for (tc = 0; tc < RTE_SCHED_TRAFFIC_CLASSES_PER_PIPE; tc++) {
+			if (subport->tc_credits[tc] < 0)
+				subport->tc_credits[tc] +=
+					subport->tc_credits_per_period[tc];
+			else
+				subport->tc_credits[tc] =
+					subport->tc_credits_per_period[tc];
+		}
+		/* If we've run into the next period only update the clock to
+		 * the time + tc_period so we'll replenish the tc tokens early
+		 * in the next tc_period to compensate. */
+		lapsed = port->time - subport->tc_time;
+		if (lapsed < subport->tc_period)
+			subport->tc_time += subport->tc_period;
+		else
+			subport->tc_time = port->time + subport->tc_period;
 	}
 
 	/* Pipe TCs */
 	if (unlikely(port->time >= pipe->tc_time)) {
-		pipe->tc_credits[0] = params->tc_credits_per_period[0];
-		pipe->tc_credits[1] = params->tc_credits_per_period[1];
-		pipe->tc_credits[2] = params->tc_credits_per_period[2];
-		pipe->tc_credits[3] = params->tc_credits_per_period[3];
-		pipe->tc_time = port->time + params->tc_period;
+		for (tc = 0; tc < RTE_SCHED_TRAFFIC_CLASSES_PER_PIPE; tc++) {
+			if (pipe->tc_credits[tc] < 0)
+				pipe->tc_credits[tc] +=
+					params->tc_credits_per_period[tc];
+			else
+				pipe->tc_credits[tc] =
+					params->tc_credits_per_period[tc];
+		}
+		/* If we've run into the next period only update the clock to
+		 * the time + tc_period so we'll replenish the tc tokens early
+		 * in the next tc_period to compensate. */
+		lapsed = port->time - pipe->tc_time;
+		if (lapsed < params->tc_period)
+			pipe->tc_time += params->tc_period;
+		else
+			pipe->tc_time = port->time + params->tc_period;
 	}
 }
 
@@ -1586,16 +1610,16 @@ grinder_credits_check(struct rte_sched_port *port, uint32_t pos)
 	uint32_t tc_index = grinder->tc_index;
 	uint32_t pkt_len = pkt->pkt_len + port->frame_overhead;
 	uint32_t subport_tb_credits = subport->tb_credits;
-	uint32_t subport_tc_credits = subport->tc_credits[tc_index];
+	int32_t subport_tc_credits = subport->tc_credits[tc_index];
 	uint32_t pipe_tb_credits = pipe->tb_credits;
-	uint32_t pipe_tc_credits = pipe->tc_credits[tc_index];
+	int32_t pipe_tc_credits = pipe->tc_credits[tc_index];
 	int enough_credits;
 
 	/* Check queue credits */
 	enough_credits = (pkt_len <= subport_tb_credits) &&
-		(pkt_len <= subport_tc_credits) &&
+		(subport_tc_credits > 0) &&
 		(pkt_len <= pipe_tb_credits) &&
-		(pkt_len <= pipe_tc_credits);
+		(pipe_tc_credits > 0);
 
 	if (!enough_credits)
 		return 0;
@@ -1603,8 +1627,8 @@ grinder_credits_check(struct rte_sched_port *port, uint32_t pos)
 	/* Update port credits */
 	subport->tb_credits -= pkt_len;
 	subport->tc_credits[tc_index] -= pkt_len;
-	pipe->tb_credits -= pkt_len;
 	pipe->tc_credits[tc_index] -= pkt_len;
+	pipe->tb_credits -= pkt_len;
 
 	return 1;
 }
-- 
2.7.4