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Monthly Archives: October 2012

Turbo-charge View Video Performance

For desktop VMs using VMXnet3 NICs, you can significantly improve the peak video playback performance of your View desktop by simply setting the following registry setting to the value recommended by Microsoft:

HKLM\System\CurrentControlSet\Services\Afd\Parameters\FastSendDatagramThreshold to 1500

[As discussed in a Microsoft KB article here]

[N.B. A reboot of the desktop VM is required after changing this registry setting]

When running full-screen videos at 1080p resolution on a 2vCPU desktop, we see this deliver frame-rate improvements of up to 1.4X.

So, what does this do and why does it deliver these benefits?

The VMXNET3 adapter is a paravirtualized NIC designed for performance that, as of vSphere 5, supports interrupt coalescing. Virtual interrupt coalescing is similar to a physical NICs interrupt moderation and is useful in improving CPU efficiency for high throughput workloads. Unfortunately, out-of-the-box, Windows does not benefit from interrupt coalescing in many scenarios (those sending packets larger than 1024-bytes), because after sending a packet, Windows waits for a completion interrupt to be delivered before sending the next packet. By setting ParametersFastSendDatagramThreshold to the Microsoft recommended value of 1500 bytes you instruct Windows not to wait for the completion interrupt even when sending larger packets. Accordingly, you are allowing View and PCoIP (as well as other applications that send larger packets) to benefit from interrupt coalescing – reducing CPU load and improving network throughput for PCoIP  — which translates into significantly improved video playback performance.