Packet latency based arbitration technique for a packet switch

A packet switch, comprising:

• a plurality of output ports;
• a plurality of input ports, each input port of the plurality of input ports configured to receive a data packet including data units and identify a destination output port of the plurality of output ports for the data packet;
• a switch fabric coupled to the plurality of input ports and the plurality of output ports, the switch fabric comprising a buffered crossbar including a plurality of crosspoints each configured to store at least one data unit of a data packet;
• a plurality of credit counters corresponding to the plurality of crosspoints and configured to store a corresponding plurality of credit values for the plurality of crosspoints;
• a plurality of latency counters corresponding to the plurality of crosspoints;
• and
• an arbiter coupled to the plurality of output ports, the plurality of credit counters, and the plurality of latency counters, the arbiter configured to select a crosspoint of the plurality of crosspoints in a plurality of nonconsecutive arbitration cycles based on the plurality of credit values, the selected crosspoint further configured to route a data packet received at the selected crosspoint to the destination output port of the data packet in the plurality of nonconsecutive arbitration cycles by routing a data unit of the data packet in each arbitration cycle of the plurality of nonconsecutive arbitration cycles, the arbiter further configured to measure a latency for routing the data packet received at the selected crosspoint from the selected crosspoint to the destination output port of the data packet by starting the latency counter corresponding to the selected crosspoint for a first data unit of the data packet routed from the selected crosspoint to the destination output port and stopping the latency counter corresponding to the selected crosspoint for a last data unit of the data packet routed from the selected crosspoint to the destination output port such that the latency counter corresponding to the selected crosspoint indicates the measured latency, the arbiter further configured to modify the credit value of the selected crosspoint for reducing variance among latencies of data packets subsequently routed through the packet switch, wherein the latency for routing the data packet from the selected crosspoint to the destination output port of the data packet is equal to a number of clock cycles of a clock signal spanning a time period for routing the data packet from the selected crosspoint to the destination output port of the data packet.

A method of routing data packets through a packet switch, the method comprising:

• receiving data packets including data units at a plurality of input ports of a packet switch;
• identifying a destination output port of a plurality of output ports in the packet switch for each of the data packets;
• storing a data unit of each of the data packets in a corresponding crosspoint of a plurality of crosspoints in a switch fabric of the packet switch;
• selecting a crosspoint of the plurality of crosspoints in a plurality of nonconsecutive arbitration cycles based on the plurality of credit values;
• routing a data packet from the selected crosspoint to the destination output port of the data packet in the plurality of nonconsecutive arbitration cycles by routing a data unit of the data packet in each arbitration cycle of the plurality of nonconsecutive arbitration cycles;
• measuring a latency for routing the data packet from the selected crosspoint to the destination output port of the data packet by starting a latency counter corresponding to the selected crosspoint for a first data unit of the data packet routed from the selected crosspoint and stopping the latency counter corresponding to the selected crosspoint for a last data unit of the data packet routed from the selected crosspoint such that the latency counter corresponding to the selected crosspoint indicates the measured latency;
• and
• modifying the credit value of the selected crosspoint based on the measured latency for reducing variance among latencies of data packets subsequently routed through the packet switch,
• wherein the latency for routing the data packet from the selected crosspoint to the destination output port of the data packet is equal to a number of clock cycles of a clock signal spanning a time period for routing the data packet from the selected crosspoint to the destination output port of the data packet.