Dell S5000 FTOS 9.0(1.3) Configuration Guide for the Switch - Page 1026

www.dell.com | support.dell.com 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 application-specific integrated circuits (ASICs) implement the key functions of queuing, feature lookups, and forwarding lookups in the hardware. Forwarding Processor (FP) ASICs provide Ethernet MAC functions, queueing and buffering, and store feature and forwarding tables for hardware-based lookup and forwarding decisions. 10G and 40G interfaces use different FPs. You can tune buffers at three locations, as shown in Figure 56-8. 1. ConfigServer Firewall (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, four for data traffic and four for control traffic. All eight 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 • Available packet pointers (2k per interface). Each packet is managed in the buffer using a unique packet pointer. Thus, each interface can manage up to 2k packets. You can configure dynamic buffers per port on both 1G and 10G FPs and per queue on CSFs. By default, the FP dynamic buffer allocation is 10 times oversubscribed. For the 48-port 1G unit: • Dynamic Pool= Total Available Pool(16384 cells) - Total Dedicated Pool = 5904 cells • Oversubscription ratio = 10 • Dynamic Cell Limit Per port = 59040/29 = 2036 cells 1026 | S5000 Debugging and Diagnostics