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scalable networking pack

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In late 2007 we have released an important feature update to the existing network stack on 2003 machines that contains the following technologies:

 

  • TCP Chimney offload
  • Receive Side Scaling (RSS)
  • Network Direct Memory Access (NetDMA)

Modern networked servers that run on the latest hardware like the PCIe bus and the associated new MSI interrupt technologies will take advantage of technologies like the RSS and NetDMA. TCP Chimney offloading helps with reassembly of TCP streams and offloads all TCP related computation to the NIC on-board processor thereby reducing the workload on the CPU and RSS will enable better handling and load distribution of incoming NIC interrupts in multiprocessor systems.

The details of these technologies are covered in a number of places in this white paper and KB912222, "The Microsoft Windows Server 2003 Scalable Networking Pack release" and KB936594, "You may experience network-related problems after you install Windows Server 2003 SP2 or the Scalable Networking Pack on a Windows Server 2003-based computer".

As this is a framework that is built to integrate a software function that to be offloaded to hardware, tight integration with the NIC hardware and associated drivers are there. Due the complexity and nature of this integration, and partly due to the fact that the above mentioned 3 technology frameworks being fairly new, with certain deployments we have faced issues where the workaround moving forward was to disable this feature on that server. Is it a concern to disable these features?

Not really, for most of the deployments out there this technology is not required.  Most servers will not see any performance benefit at all by deploying this technology. Let's say that you have a very busy file server with a NIC that is %80 utilized at all times. If on this server you don't see the processor utilization around the same numbers, then you'll probably not see any difference in performance after applying this pack on that server. The main benefit will be with servers that have multiple processors, huge number of files to serve that have multiple network cards and are serving couple gigs bps. These servers will benefit from RSS in utilizing all processors in processing the MSI interrupts and distributing them equally among all processors, by offloading the TCP work to the NIC and they will perform much better when the load is more than a regular networked server.

In summary it would be safe to say that when you have issues with the scalable networking pack, either due the problem described in 936594 or because you have an incompatibility with the network hardware, it is advisable to contact Microsoft PSS and in the meantime remove the features enabled by this pack. It is important to monitor a server's network and processor performance before going forward to enable this feature set on a server, as described above there are only certain scenarios coupled with a high load on CPU usage in a system where this will be useful.