Adaptive allocation of headroom in network devices

1. Communication apparatus, comprising:

multiple ports configured for connection to a packet data network;

a memory coupled to the ports and configured to contain, for each port, a respective first, fixed headroom allocation to hold packets received from the network through the port and to contain a shared headroom buffer, which is available to be shared among a plurality of the ports; and

flow-control logic, which is configured to allocate to each of the ports, within the shared headroom buffer, a respective second, variable headroom allocation, which varies responsively to fill levels of the respective first headroom allocation and of the shared headroom buffer, thereby defining, for each of the ports, a respective total headroom allocation comprising the respective first and second headroom allocations, and which is configured to apply flow-control operations in response to the packets received from the network through each port responsively to a size of and a total fill level of the respective total headroom allocation of the port.

2. The apparatus according to claim 1 , wherein the flow-control logic is configured to set a threshold for each port responsively to the respective total headroom allocation, and to apply a flow-control operation when the total fill level is above the threshold.

3. The apparatus according to claim 2 , wherein the threshold is an XOFF threshold, and wherein the flow-control operation comprises sending a PAUSE frame to a peer node when the total fill level passes the XOFF threshold.

4. The apparatus according to claim 2 , wherein the threshold is an XON threshold, and wherein the flow-control operation comprises sending a command to a peer node to resume transmission of packets when the total fill level drops below the XON threshold.

5. The apparatus according to claim 2 , wherein the threshold is drop threshold, and wherein the flow-control operation comprises dropping one or more packets received from a peer node when the total fill level passes the drop threshold.

6. The apparatus according to claim 1 , wherein the first, fixed headroom allocation comprises, for each port, multiple, respective sub-allocations, which are respectively assigned to different flow-control classes of the packets received through the port, and wherein at least a part of the respective second, variable headroom allocation of the port is shared among the different flow-control classes.

7. The apparatus according to claim 6 , wherein the flow-control logic is configured to allocate to each port, within the shared headroom buffer, a third headroom allocation, which is shared among the different flow-control classes of the packets received through the port, in addition to the respective sub-allocations of the first, fixed headroom allocation that are assigned to the different flow-control classes and to the part of the respective second, variable headroom allocation of the port.

8. A method for communication, comprising:

in a network element having multiple ports connected to a packet data network and a memory coupled to the ports, providing to each port a respective first, fixed headroom allocation in the memory to hold packets received from the network through the port, and providing in the memory a shared headroom buffer, which is available to be shared among a plurality of the ports;

allocating to each of the ports, within the shared headroom buffer, a respective second, variable headroom allocation, which varies responsively to fill levels of the respective first headroom allocation and of the shared headroom buffer, thereby defining, for each of the ports, a respective total headroom allocation comprising the respective first and second headroom allocations; and

applying flow-control operations in response to the packets received from the network through each port responsively to a size of and a total fill level of the respective total headroom allocation of the port.

9. The method according to claim 8 , wherein applying the flow-control operations comprises setting a threshold for each port responsively to the respective total headroom allocation, and performing a flow-control operation when the total fill level is above the threshold.

10. The method according to claim 9 , wherein the threshold is an XOFF threshold, and wherein the flow-control operation comprises sending a PAUSE frame to a peer node when the total fill level passes the XOFF threshold.

11. The method according to claim 9 , wherein the threshold is an XON threshold, and wherein the flow-control operation comprises sending a command to a peer node to resume transmission of packets when the total fill level drops below the XON threshold.

12. The apparatus according to claim 9 , wherein the threshold is drop threshold, and wherein the flow-control operation comprises dropping one or more packets received from a peer node when the total fill level passes the drop threshold.

13. The method according to claim 8 , wherein the first, fixed headroom allocation comprises, for each port, multiple, respective sub-allocations, which are respectively assigned to different flow-control classes of the packets received through the port, and wherein at least a part of the respective second, variable headroom allocation of the port is shared among the different flow-control classes.

14. The method according to claim 13 , wherein applying the flow-control operations comprises allocating to each port, within the shared headroom buffer, a third headroom allocation, which is shared among the different flow-control classes of the packets received through the port, in addition to the respective sub-allocations of the first, fixed headroom allocation that are assigned to the different flow-control classes and to the part of the respective second, variable headroom allocation of the port.