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Configuring Global Ingress and Egress Shared Buffers

Although the switch reserves some buffer space to ensure a minimum memory allocation for ports and queues, you can configure how the system uses the rest of the buffer space to optimize the buffer allocation for your particular mix of network traffic. The global shared buffer pool is memory space that all of the ports on the switch share dynamically as they need buffers. You can allocate global shared memory space to different types of ingress and egress buffers to better support different mixes of network traffic.

CAUTION:

Changing the buffer configuration is a disruptive event. Traffic stops on all ports until buffer reprogramming is complete.

Use the default shared buffer settings (for a network with a balanced mix of lossless, best-effort, and multicast traffic) or one of the recommended shared buffer configurations for your mix of network traffic (mostly best-effort unicast traffic, mostly best-effort traffic on links enabled for Ethernet PAUSE, mostly multicast traffic, or mostly lossless traffic). Either the default configuration or one of the recommended configurations provides a buffer allocation that satisfies the needs of most networks.

After starting from one of the recommended configurations, you can fine-tune the shared buffer settings, but do so with caution to prevent traffic loss due to buffer misconfiguration.

You can configure the percentage of available (user-configurable) buffer space allocated to the global shared buffers. Any space that you do not allocate to the global shared buffer pool is added to the dedicated buffer pool. The default configuration allocates 100 percent of the available buffer space to the global shared buffers.

You can partition the ingress and egress shared buffer pools to allocate more buffers to the types of traffic your network predominantly carries, and fewer buffers to other traffic. From the buffer space allocated to the ingress shared buffer pool, you can allocate space to:

  • Lossless buffers—Percentage of shared buffer pool for all lossless ingress traffic. The minimum value for the lossless buffers is 5 percent.

  • Lossless headroom buffers—Percentage of shared buffer pool for packets received while a pause is asserted. If Ethernet PAUSE is configured on a port or if priority-based flow control (PFC) is configured on priorities on a port, when the port sends a pause message to the connected peer, the port uses the headroom buffers to store the packets that arrive between the time the port sends the pause message and the time the last packet arrives after the peer pauses traffic. The minimum value for the lossless headroom buffers is 0 (zero) percent. (Lossless headroom buffers are the only buffers that can have a minimum value of less than 5 percent.)

  • Lossy buffers—Percentage of shared buffer pool for all best-effort ingress traffic (best-effort unicast, multidestination, and strict-high priority traffic). The minimum value for the lossy buffers is 5 percent.

The combined percentage values of the ingress lossless, lossless headroom, and lossy buffer partitions must total exactly 100 percent. If the buffer percentages total more than 100 percent or less than 100 percent, the switch returns a commit error. All ingress buffer partitions must be explicitly configured, even when the lossless headroom buffer partition has a value of 0 (zero) percent.

From the buffer space allocated to the egress shared buffer pool, you can allocate space to:

  • Lossless buffers—Percentage of shared buffer pool for all lossless egress queues. The minimum value for the lossless buffers is 5 percent.

  • Lossy buffers—Percentage of shared buffer pool for all best-effort egress queues (best-effort unicast and strict-high priority queues). The minimum value for the lossy buffers is 5 percent.

  • Multicast buffers—Percentage of shared buffer pool for all multidestination (multicast, broadcast, and destination lookup fail) egress queues. The minimum value for the multicast buffers is 5 percent.

The combined percentage values of the egress lossless, lossy, and multicast buffer partitions must total exactly 100 percent. If the buffer percentages total more than 100 percent or less than 100 percent, the switch returns a commit error. All egress buffer partitions must be explicitly configured and must have a value of at least 5 percent.

To configure the shared buffer allocation and partitioning using the CLI:

  1. Configure the percentage of available (nonreserved) buffers used for the ingress global shared buffer pool:

  2. Configure the global ingress buffer partitions for lossless, lossless-headroom, and lossy traffic:

  3. Configure the percentage of available (nonreserved) buffers used for the egress global shared buffer pool:

  4. Configure the global egress buffer partitions for lossless, lossy, and multicast queues: