Adaptive routing based on flow-control credits
A method for network communication includes receiving in a network element a packet for forwarding to a destination node. The destination node is reachable via two or more candidate ports of the network element that are connected to respective next-hop network elements. Link-level flow-control credit notifications are received in the network element from the next-hop network elements via the respective candidate ports. An egress port is selected for the packet, from among the candidate ports, based at least on the received link-level flow-control credit notifications. The packet is forwarded toward the destination node over the selected egress port.
1. A method for network communication, comprising:
in a network element, receiving a packet for forwarding to a destination node, wherein the destination node is reachable via two or more candidate ports of the network element that are connected to respective next-hop network elements;
receiving in the network element link-level flow-control credit notifications from the next-hop network elements via the respective candidate ports;
selecting an egress port for the packet from among the candidate ports, based at least on the received link-level flow-control credit notifications, by:
deriving, from the received link-level flow-control credit notifications, numbers of credits that are currently available on the candidate ports;
normalizing the numbers of credits by respective lengths of network links that connect the next-hop network elements to the candidate ports; and
selecting the egress port based at least on the normalized numbers of credits; and
forwarding the packet toward the destination node over the selected egress port.
2. The method according to claim 1 , wherein selecting the egress port comprises calculating, based at least on the link-level flow-control credit notifications, port congestion grades for the candidate ports, and selecting the egress port based on the port congestion grades.
3. The method according to claim 1 , wherein the packet is associated with a given Virtual Lane (VL), and wherein selecting the egress port comprises choosing the egress port only based on the link-level flow-control credit notifications pertaining to the given VL.
4. The method according to claim 1 , wherein the packet is associated with a given Virtual Lane (VL), and wherein selecting the egress port comprises choosing the egress port based on (i) the link-level flow-control credit notifications pertaining to the given VL, and (ii) the link-level flow-control credit notifications pertaining to the candidate ports as a whole.
5. The method according to claim 1 , and comprising, in addition to selecting the egress port, throttling amounts of data sent via the candidate ports based on the received link-level flow-control credit notifications.
6. A network element, comprising:
multiple ports; and
circuitry, configured to:
receive a packet for forwarding to a destination node, wherein the destination node is reachable via two or more candidate ports of the network element that are connected to respective next-hop network elements;
receive link-level flow-control credit notifications from the next-hop network elements via the respective candidate ports;
select an egress port for the packet from among the candidate ports, based at least on the received link-level flow-control credit notifications, by:
deriving, from the received link-level flow-control credit notifications, numbers of credits that are currently available on the candidate ports;
normalizing the numbers of credits by respective lengths of network links that connect the next-hop network elements to the candidate ports; and
selecting the egress port based at least on the normalized numbers of credits; and
forward the packet toward the destination node over the selected egress port.
7. The network element according to claim 5 , wherein the circuitry is configured to calculate, based at least on the link-level flow-control credit notifications, port congestion grades for the candidate ports, and to select the egress port based on the port congestion grades.
8. The network element according to claim 5 , wherein the packet is associated with a given Virtual Lane (VL), and wherein the circuitry is configured to select the egress port only based on the link-level flow-control credit notifications pertaining to the given VL.
9. The network element according to claim 5 , wherein the packet is associated with a given Virtual Lane (VL), and wherein the circuitry is configured to select the egress port based on (i) the link-level flow-control credit notifications pertaining to the given VL, and (ii) the link-level flow-control credit notifications pertaining to the candidate ports as a whole.
10. The network element according to claim 5 , wherein, in addition to selecting the egress port, the circuitry is further configured to throttle amounts of data sent via the candidate ports based on the received link-level flow-control credit notifications.
11. A computer software product, the product comprising a tangible non-transitory computer-readable medium in which program instructions are stored, which instructions, when read by a processor in a network element, cause the processor to:
receive a packet for forwarding to a destination node, wherein the destination node is reachable via two or more candidate ports of the network element that are connected to respective next-hop network elements;
receive link-level flow-control credit notifications from the next-hop network elements via the respective candidate ports;
select an egress port for the packet from among the candidate ports, based at least on the received link-level flow-control credit notifications, by:
deriving, from the received link-level flow-control credit notifications, numbers of credits that are currently available on the candidate ports;
normalizing the numbers of credits by respective lengths of network links that connect the next-hop network elements to the candidate ports; and
selecting the egress port based at least on the normalized numbers of credits; and
forward the packet toward the destination node over the selected egress port.