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Configuring Ingress and Egress Dedicated Buffers

SUMMARY This topic describes how to adjust the size of the dedicated buffer, both globally and on a per-port basis.

The switch partitions its buffer into dedicated and shared buffers. As the name suggests, the dedicated buffer is exclusive to each port and only that port can use its dedicated buffer. The shared buffer is shared across all ports. When there is little traffic on many ports and few ports have bursty traffic, the dedicated buffers of the ports carrying little traffic are unused, and bursty traffic ports cannot use these unused buffers.

However, you can decrease the global dedicated buffer space from the default value, effectively increasing the global shared buffer space so that bursty traffic ports can use more of the buffer space according to their dynamic-threshold value.

You can also define a dedicated buffer profile to increase or decrease the dedicated buffer allocated to an individual port. This is particularly useful for decreasing dedicated buffer space on unused or down ports, thereby increasing dedicated buffer space available to active ports.

You can fine-tune the dedicated buffer settings, but do so with caution to prevent traffic loss due to buffer misconfiguration.

Decreasing the Global Dedicated Buffer

Set the global dedicated buffer pool of the device as a percent of its default. This, in effect, increases the shared buffer pool. The percentage can range from 15 to 100 percent of the default. The minimum of 15 percent is to ensure that each port receives some amount of minimal dedicated buffer to reduce the probability of all ports contending for the shared buffer.

Note:

You can decrease the dedicated-buffer (thereby increasing the shared buffer pool), or decrease the shared-buffer (thereby increasing the dedicated buffer pool), but not both.
  1. Check the current dedicated and shared buffer allocation.

    For example:

  2. Set the global egress dedicated buffer size as a percentage of its default, from 15 to 100 percent.

    For example:

  3. Set the global ingress dedicated buffer size as a percentage of its default, from 15 to 100 percent.

    For example:

  4. Commit your changes.
  5. Verify your configuration.

    For example:

  6. Check the shared buffer to verify both the dedicated buffer and shared buffer have changed according to the configuration.

    For example:

Notice how the ingress and egress dedicated buffers are now less and the shared buffer has increased while the total buffer remains the same.

Configuring and Applying Dedicated Buffer Profiles

By default, the operating system calculates port level dedicated buffers internally. Therefore, even ports that are down or unused also get an equal amount of dedicated buffer space that is then unavailable to any traffic burst. The dedicated buffer profile provides the ability to increase or decrease the default dedicated buffer at a physical interface level.

With the dedicated buffer profile you can separately set the ingress and egress dedicated buffer size to be a number of cells, with each cell being 254 bytes. You can also set the ingress and egress dedicated buffer size to be none. Setting the dedicated buffer size to none is useful for unused or down ports. Note that when a port with no dedicated buffer becomes congested, the port directly consumes from the shared buffer pool.

Once you define a dedicated buffer profile, you can attach it directly to a physical interface.

Remaining dedicated buffers that you do not allocate to any ports by a dedicated buffer profile are equally shared among ports (based on speed) that don't have a dedicated buffer profile assigned to them.

Note:

You cannot assign a dedicated-buffer-profile to aggregated Ethernet (ae-) interfaces. You can only assign a dedicated-buffer-profile to a physical interface.
CAUTION:

If the buffer-size of all dedicated buffer profiles combined exceeds the total available dedicated buffer pool, the system logs a syslog error and does not implement the new configuration even though the commit succeeds.
  1. Set the name and egress buffer size of the dedicated-buffer-profile .

    For example:

  2. Set the ingress buffer size of the dedicated buffer profile.

    For example:

  3. Commit your changes.
  4. Apply the dedicated buffer profile to an interface.

    For example:

  5. Verify your configuration.

    For example:

  6. Use show commands to verify the presence of the dedicated buffer profile.

    For example:

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