Buffer Tuning - Dell Force10 C150 Configuration Manual

Buffer tuning

Buffer Tuning allows you to modify the way your switch allocates buffers from its available memory, and
helps prevent packet drops during a temporary burst of traffic.
The C-Series and S-Series ASICs implement the key functions of queuing, feature lookups, and
forwarding lookups in hardware.
• Forwarding Processor (FP) ASICs provide Ethernet MAC functions, queueing and buffering, as well
as store feature and forwarding tables for hardware-based lookup and forwarding decisions. 1G and
10G interfaces use different FPs.
• Switch Fabric (CSF) ASICs are on the C-Series only. They provide some queuing while also providing
the physical pathway through which frames are switched between ports when the source and
destination ports are attached to different FP ASICs.
Table 60-5 describes the type and number of ASICs per platform.
You can tune buffers at three locations, as shown in
1. CSF – Output queues going from the CSF.
2. FP Uplink—Output queues going from the FP to the CSF IDP links.
3. Front-End Link—Output queues going from the FP to the front-end PHY.
All ports support eight queues, 4 for data traffic and 4 for control traffic. All 8 queues are tunable.
Physical memory is organized into cells of 128 bytes. The cells are organized into two buffer pools—
dedicated buffer and dynamic buffer.
• Dedicated buffer is reserved memory that cannot be used by other interfaces on the same ASIC or by
other queues on the same interface. This buffer is always allocated, and no dynamic recarving takes
place based on changes in interface status. Dedicated buffers introduce a trade-off. They provide each
interface with a guaranteed minimum buffer to prevent an overused and congested interface from
starving all other interfaces. However, this minimum guarantee means the buffer manager does not
reallocate the buffer to an adjacent congested interface, which means that in some cases, memory is
underused.
• Dynamic buffer is shared memory that is allocated as needed, up to a configured limit. Using dynamic
buffers provides the benefit of statistical buffer sharing. An interface requests dynamic buffers when
its dedicated buffer pool is exhausted. The buffer manager grants the request based on three
conditions:
• the number of used and available dynamic buffers
• the maximum number of cells that an interface can occupy
Table 60-5. ASICS by Platform
Hardware
48-port LC on C-Series
FP CSF
2 2
Figure 60-18.
C-Series Debugging and Diagnostics | 1189