Administrator Guide

Physical memory is organized into cells of 128 bytes. The cells are organized into two buer pools — the dedicated buer and the
dynamic buer.
• Dedicated buer — this pool is reserved memory that other interfaces cannot use on the same ASIC or by other queues on the
same interface. This buer is always allocated, and no dynamic re-carving takes place based on changes in interface status.
Dedicated buers introduce a trade-o. They provide each interface with a guaranteed minimum buer to prevent an overused
and congested interface from starving all other interfaces. However, this minimum guarantee means that the buer manager
does not reallocate the buer to an adjacent congested interface, which means that in some cases, memory is under-used.
• Dynamic buer — this pool is shared memory that is allocated as needed, up to a congured limit. Using dynamic buers
provides the benet of statistical buer sharing. An interface requests dynamic buers when its dedicated buer pool is
exhausted. The buer manager grants the request based on three conditions:
– The number of used and available dynamic buers.
– The maximum number of cells that an interface can occupy.
– Available packet pointers (2k per interface). Each packet is managed in the buer using a unique packet pointer. Thus, each
interface can manage up to 2k packets.
You can congure dynamic buers per port on both 1G and 10G FPs and per queue on CSFs. By default, the FP dynamic buer
allocation is 10 times oversubscribed. For the 48-port 1G card:
• Dynamic Pool= Total Available Pool(16384 cells) — Total Dedicated Pool = 5904 cells
• Oversubscription ratio = 10
• Dynamic Cell Limit Per port = 59040/29 = 2036 cells
Figure 36. Buer Tuning Points
Deciding to Tune Buers
Dell Networking recommends exercising caution when conguring any non-default buer settings, as tuning can signicantly aect
system performance. The default values work for most cases.
As a guideline, consider tuning buers if trac is bursty (and coming from several interfaces). In this case:
274
Debugging and Diagnostics