Method and apparatus for reducing pool starvation in a shared memory switch
View Patent ↗A switch includes a reserved pool of buffers in a shared memory. The reserved pool of buffers is reserved for exclusive use by an egress port. The switch includes pool select logic which selects a free buffer from the reserved pool for storing data received from an ingress port to be forwarded to the egress port. The shared memory also includes a shared pool of buffers. The shared pool of buffers is shared by a plurality of egress ports. The pool select logic selects a free buffer in the shared pool upon detecting no free buffer in the reserved pool. The shared memory may also include a multicast pool of buffers. The multicast pool of buffers is shared by a plurality of egress ports. The pool select logic selects a free buffer in the multicast pool upon detecting an IP Multicast data packet received from an ingress port.
1. A method comprising:
logically portioning a shared memory into a number of reserved pools and other pools, the other pools including a multicast pool for storing only multicast data packets to be forwarded to at least one egress port to members of a multicast group;
receiving a number of buffer pool selection determinants, said selection determinants including counter status information and egress port forwarding information, said egress port forwarding information dependent upon a header of an accepted data packet to be stored in a buffer;
selecting either one of the reserved pools or one of the other pools from which to allocate the buffer for data based on said selection determinants, and said egress port forwarding information having consequence on the selecting of the pool when the selecting is from the reserved pools; and
allocating the buffer from the selected pool.
2. The method as claimed in claim 1 wherein the egress port forwarding information includes a forward vector indicating which egress port to forward a data packet.
3. The method as claimed in claim 1 wherein the counter status information includes at least one of the following: total free counter, multicast free counter, shared free counter, reserved free counter, a plurality of port reserve pool counters, and at least one queue reserved threshold counter.
4. The method as claimed in claim 1 further comprising: determining how shared memory is divided to reduce the probability of dropping data packets.
5. A switch comprising:
a plurality of egress ports;
a shared memory configured to be logically portioned into reserved pools of buffers and other pools of buffers, and each one of the reserved pools of buffers being reserved for a respective one of the egress ports, and the other pools of buffers including a multicast pool of buffers reserved to store only multicast packets to be forwarded to an at least one of the egress ports to members of a multicast group;
an information receiver for receiving a number of buffer pool selection determinants, said selection determinants including counter status information and egress port forwarding information, said egress port forwarding information dependent upon a header of an accepted data packet to be stored in a buffer; and
logic for selecting either one of the reserved pools or one of the other pools from which to allocate the buffer for data based on said selection determinants, and said egress port forwarding information having consequence on the selecting of the pool when the logic selects from the reserved pools.
6. The switch as claimed in claim 5 wherein the egress port forwarding information includes a forward vector indicating which egress port to forward a data packet.
7. The switch as claimed in claim 5 wherein the counter status information includes at least one of the following: total free counter, multicast free counter, shared free counter, reserved free counter, a plurality of port reserve pool counters, and at least one queue reserved threshold counter.
8. The switch as claimed in claim 5 further comprising a plurality of ingress ports.