Passing a command from the application to the OS requires a CPU intensive context switch. When executing a context switch, the CPU must save the application context in system memory, including all of the CPU general-purpose registers, floating-point registers, stack pointers, the instruction pointer, and all of the memory-management-unit state associated with the application’s memory access rights. Then the OS context is restored by loading a similar set of items for the OS from system memory.
The iWARP extensions implement OS bypass (user-level direct access), enabling an application executing in user space to post commands directly to the network adapter (Fig. 4). This eliminates expensive calls to the OS, dramatically reducing application context switches. An accelerated Ethernet adapter handles tasks typically performed by the OS. Such adapters are more complex than traditional non-accelerated NICs, but can eliminate the final 40% of CPU overhead related to networking.
POTENTIAL APPLICATIONS
Clustered servers/blades depend on high-bandwidth, low-latency interconnects to aggregate the enormous processing power of dozens of CPUs and keep I/O needs serviced. For these applications, iWARP is advantageous because it delivers:
• Predictable, sustained, scalable performance, even in multicore, multi-processor clusters
• A single, self-provisioning adapter that supports all clustering MPIs: HP MPI, Intel MPI, Scali MPI, MVAPICH2
• Modern low-latency interconnect technologies to an ultra-lowpower, high-bandwidth Ethernet package; flexibility, cost, and industry-standard management benefits; and exceptional processing power per square foot for clustered applications.
For data-networking applications, iWARP-based accelerated Ethernet adapters offer full-function data-center NIC capabilities that boost performance, improve power efficiency, and more fully utilize data-center assets. The accelerated Ethernet adapters achieve the highest throughput, lowest latency, and lowest power consumption in the industry.
In particular, when it comes to network overhead processing, it achieves 95% CPU availability for the application and operating system. In addition, hardware-class performance for virtualized applications ensures offloaded CPU cycles from network processing are not lost to software-virtualization overhead.
For storage vendors, iWARP will become a standard feature of network-attached storage (NAS) and Internet small computer systems interface (iSCSI) storage access networks (SANs). NAS and iSER-based (iSCSI Extensions for RDMA) storage networks utilizing accelerated Ethernet adapters deliver the highestperformance, lowest-overhead storage solutions at any given wire rate.
At 10 Gbits/s, Ethernet-based storage networks offer a viable alternative to a Fibre Channel SAN. There’s a single network interface for block and file protocols, high-throughput block, and file-level storage access, exceeding 8-Gbit Fibre Channel.
In addition to iSCSI, iWARP supports a wide range of other storage protocols such as network file system (NFS) and common Internet file system (CIFS). This gives data centers the opportunity to reap the increased productivity and lowered total cost of ownership benefits of a ubiquitous, standards-based technology.
Like InfiniBand, iWARP does not have a standard programming interface, only a set of verbs. Unlike the InfiniBand architecture (IBA), iWARP only has reliable connected communication as this is the only service that TCP and SCTP provide. The iWARP specification also omits many of the special features of IBA, such as atomic remote operations. In all, iWARP offers the basics of InfiniBand applied to Ethernet. This suits it well for both legacy software and next-generation applications.