6–Configuring NIC Functionality in the Converged Network AdapterConfiguring the NIC in a Windows Environment6-10 FE0254601-00 Aabout the CheckSumOffload parameter, refer to Table 6-1 Do not turn offchecksum offload unless you are debugging a checksum computationproblem. TCP checksum offloading significantly reduced reduces host CPUuse when using jumbo frames. Stateless offload—QLogic 8100 Series Adapters support large sendoffloading (LSO).LSO enables the Microsoft Windows TCP stack to sendone large block of data to the QLogic adapter, which then segments thislarge block into multiple TCP packets. The LargeSendOffloadSupportparameter is enabled by default and can be disabled on the WindowsAdvanced property pages for the QLogic 10Gb PCI Ethernet adapter usingWindows Device Manager. For information about theLargeSendOffloadSupport parameter, refer to Table 6-1.Receive Side ScalingQLogic 8100 Series Adapters supports receive side scaling (RSS) in MicrosoftWindows environments for nonoffloaded IP/TCP traffic. When a packet arrives ona network interface, an interrupt is sent to the network driver. The network driverthen executes a deferred procedure call (DPC), which runs on the same CPU asthe interrupt. With RSS disabled, only one DPC can execute at a time. With RSSenabled, up to four parallel DPCs can run on four different processors or cores,which enables the simultaneous receive processing of incoming packets(Figure 6-4).Figure 6-4. Receive Side Scaling ConceptsWith RSS enabled, the NIC driver implements a hash function to distributeinbound packets across CPUs. In-order delivery is maintained by identifying theflow. RSS provides the following advantages: Parallel processing of inbound packets while maintaining in-order delivery Load balancing of network processing across CPUs in an symmetricalmultiprocessing (SMP) system Cache locality
