Users Guide

Table 18. Buer usage statistics when shared headroom is used
Parameter Description
PFC Shared buer size 208 KB
Buer-size parameter of dcb-buer-threshold per
lossless queue
18KB
Pause-threshold parameter of dcb-buer-threshold
per lossless queue
18KB
Average Headroom value reserved per lossless
queue
35KB [Considering 76KB as worst case value]
Total Headroom buer to be congured in Shared
Headroom Pool
12*2*35 = 840KB
Total buer required for 2 lossless queues on 12
ports
12*2*18 + 208 + 840 = 1480KB
Shared PG headroom buer approach saves 984KB from the traditional dedicated PG headroom approach for the same number of lossless
queues. The excess buer can either be assigned to PFC shared buer size (to reduce the PFC aggressiveness) or to the lossy pool to
eectively manage lossy trac.
NOTE: When only few lossless queues are congured, the Shared headroom pool must be congured carefully to avoid any
ingress MMU drops due to insucient headroom buer.
Conguring Shared Head Room Buer
You can congure a shared head room pool limit, which is the threshold value for the shared head room pool size.
To congure the shared head room pool size:
Enter the following command in global conguration mode:
CONFIGURATION Mode
dcb pfc-headroom-buffer-size buffer-size
NOTE
: Earlier head room implementations are derived from the buer-size and pause-threshold attributes of the dcb-
buer-threshold prole. However, with the introduction of the shared head room feature, the buer-size attribute is
now obsolete as the head room buer is now global and is shared among all lossless queues or PGs. Any value
congured for buer-size is internally replaced with value congured for the pause-threshold attribute. The peak-head
room attribute continue to be the ingress threshold limit for bursty trac. This attribute determines the maximum
buer a PG can use from the shared head room pool.
Viewing Shared Head Room Usage
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
Data Center Bridging (DCB)
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