Tuesday, 12 May 2015

Battling poor network performance and/or high network latency with Receive Side Scaling

Receive Side Scaling (RSS) is a mechanism that allows the networking driver to spread TCP traffic accross acorss multiple CPUs - hence allowing multi-core efficiency and processeros cahce utilization.

Although your operating system and driver must support it - if it is not supported all network traffic is handled by the 1 CPU.

In order to utilize RSS you must firstly meet the following conditions:

- Virtual Machine hardware must be version 7 or higher
- The virtual network card you want to utilize it on MUST be VMXNET3
- Run a supported operating system: Server 2003 SP2 - Server 2012 R2 and Linux 2.6.37+.

Considerations: Although it is supported and enabled by default in the above Windows Operating systems - it is more often than not enabled by default on the virtual nic itself! So we must enable it on the virtual nic by going to NIC Properties >> Advanced >> Recieve Side Scaling >> Enabled.

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