Named Pools
Quality of Service Guide 725
A:SR7-10#
Allocation Steps
Whether one or multiple MDAs share the same buffer space, the buffer space is portioned out
on a per port basis. Each port gets an amount of buffering which is its fair-share based on the
port’s bandwidth compared to the overall active bandwidth. This is identical to current
behavior.
This mechanism takes the buffer space available and divides it into a portion for each port
based on the ports active bandwidth relative to the amount of active bandwidth for all ports
associated with the buffer space. The number of ports sharing the same buffer space depends
on the type of IOM the pools are being created on and the type of MDAs populated on the
IOM. An active port is considered to be any port that has an active queue associated. Once a
queue is created for the port, the system will allocate the appropriate amount of buffer space
to the port. This process is independently performed for both ingress and egress.
Normally, the amount of active bandwidth is considered as opposed to total potential
bandwidth for the port when determining the ports fair share. If a port is channelized and not
all bandwidth is allocated, only the bandwidth represented by the configured channels with
queues configured is counted towards the bandwidth represented by the port. Also, if a port
may operate at variable speeds (as in some Ethernet ports), only the current speed is
considered. Based on the above, the number of buffers managed by a port may change due to
queue creation and deletion, channel creation and deletion and port speed variance on the
local port or other ports sharing the same buffer space.
After the active bandwidth is calculated for the port, the result may be modified through the
use of the ‘ing-percentage-of-rate’ and ‘egr-percent-of-rate’ commands. The default value of
each is 100% which allows the system to use all of the ports active bandwidth when deciding
the relative amount of buffer space to allocate to the port. When the value is explicitly
modified, the active bandwidth on the port is changed according to the specified percentage.
If a value of 50% is given, the ports active bandwidth will be multiplied by .5; if a value of
150% is given, the active bandwidth will be multiplied by 1.5. This capability is independent
of named pool mode. The ports rate percentage parameters may be modified at any time.
When named pool mode is configured on the buffer space, the ingress and egress chunk of
buffering assigned to a port is now split into 3 smaller chunks for default pools, mda named
pools and port named pools. The way the buffering is split into the 3 smaller chunks is based
on the ‘port-allocation-weights’ given in the named-pool-policy. The weights may come from
either the XMA or MDA level applied named pool policy or the local port applied named pool
policy. If a named pool policy is assigned on both locations, the defined ‘port-allocation-
weights’ from the port associated policy will apply. Any of the weights may be set to ‘0’,
indicating that none of the buffers allocated to the port should be given to the pool category.
If only XMA or MDA named pools are created, the port weight should be set to ‘0’; if only
To Next Page
Loading...
