C-Series Debugging and Diagnostics | 1189Buffer tuningBuffer Tuning allows you to modify the way your switch allocates buffers from its available memory, andhelps prevent packet drops during a temporary burst of traffic.The C-Series and S-Series ASICs implement the key functions of queuing, feature lookups, andforwarding lookups in hardware.• Forwarding Processor (FP) ASICs provide Ethernet MAC functions, queueing and buffering, as wellas store feature and forwarding tables for hardware-based lookup and forwarding decisions. 1G and10G interfaces use different FPs.• Switch Fabric (CSF) ASICs are on the C-Series only. They provide some queuing while also providingthe physical pathway through which frames are switched between ports when the source anddestination 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 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 byother queues on the same interface. This buffer is always allocated, and no dynamic recarving takesplace based on changes in interface status. Dedicated buffers introduce a trade-off. They provide eachinterface with a guaranteed minimum buffer to prevent an overused and congested interface fromstarving all other interfaces. However, this minimum guarantee means the buffer manager does notreallocate the buffer to an adjacent congested interface, which means that in some cases, memory isunderused.• Dynamic buffer is shared memory that is allocated as needed, up to a configured limit. Using dynamicbuffers provides the benefit of statistical buffer sharing. An interface requests dynamic buffers whenits dedicated buffer pool is exhausted. The buffer manager grants the request based on threeconditions:• the number of used and available dynamic buffers• the maximum number of cells that an interface can occupyTable 60-5. ASICS by PlatformHardware FP CSF48-port LC on C-Series 2 2
