Configuring Shared Head Room Buffer; Viewing Shared Head Room Usage - Dell S6100 Configuration Manual

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Table 18. Buffer usage statistics when shared headroom is used

PFC Shared buffer size

Buffer-size parameter of dcb-buffer-threshold per

lossless queue

Pause-threshold parameter of dcb-buffer-threshold

per lossless queue

Average Headroom value reserved per lossless

Total Headroom buffer to be configured in Shared

Headroom Pool

Total buffer required for 2 lossless queues on 12

Shared PG headroom buffer approach saves 984KB from the traditional dedicated PG headroom approach for the same number of lossless

queues. The excess buffer can either be assigned to PFC shared buffer size (to reduce the PFC aggressiveness) or to the lossy pool to

effectively manage lossy traffic.

When only few lossless queues are configured, the Shared headroom pool must be configured carefully to avoid any

ingress MMU drops due to insufficient headroom buffer.

Configuring Shared Head Room Buffer

You can configure a shared head room pool limit, which is the threshold value for the shared head room pool size.

To configure the shared head room pool size:

Enter the following command in global configuration mode:

CONFIGURATION Mode

dcb pfc-headroom-buffer-size buffer-size

Earlier head room implementations are derived from the buffer-size and pause-threshold attributes of the dcb-

buffer-threshold profile. However, with the introduction of the shared head room feature, the buffer-size attribute is

now obsolete as the head room buffer is now global and is shared among all lossless queues or PGs. Any value

configured for buffer-size is internally replaced with value configured for the pause-threshold attribute. The peak-head

room attribute continue to be the ingress threshold limit for bursty traffic. This attribute determines the maximum

buffer a PG can use from the shared head room pool.

You can obtain an instantaneous usage count for the shared hear room pool.

To view the head room usage count:

Enter the following show command:

EXEC-Privilege Mode

show hardware buffer headroom-pool [detail] buffer-info

35KB [Considering 76KB as worst case value]

12*2*35 = 840KB

12*2*18 + 208 + 840 = 1480KB

Data Center Bridging (DCB)