Dell Force10 S50-01-GE-48T FTOS 8.4.2.7 Configuration Guide for E-Series TeraS - Page 1189

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. Table 60-5. ASICS by Platform Hardware FP 48-port LC on C-Series 2 CSF 2 You can tune buffers at three locations, as shown in Figure 60-18. 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 C-Series Debugging and Diagnostics | 1189