Multi-Core Scaling In A KVM Virtualized Environment

Written by Michael Larabel in Processors on 15 December 2010. Page 5 of 5. 18 Comments

The TTSIOD 3D Renderer results for the KVM Fedora 14 guest were interesting and similar to one of the GraphicsMagick results from earlier where having six or twelve cores available to the guest instance had negatively affected the performance. This was to the point that having 12 cores available to the guest running TTSIOD was at the same speed as having one core available, while four cores was the sweet spot running more than twice as fast. This is while the host Fedora 14 continued taking advantage of the extra threads on the Intel Core i7.

Lastly, with the x264 media encoding benchmark, with one and two cores enabled the performance was close between the host and guest, but the VT-x virtualized guest began to stray as the core count increased.

"Virtualization is known to work badly with virtual CPUs." So is that a fact? Not entirely. There are some cases in the results published today where the KVM guest didn't scale too well after a certain point, but there are also cases where the Kernel-based Virtual Machine guest running Fedora 14 had no problems running to the same speed as the Fedora 14 through the available 12 threads on the Intel Core i7 970 processor. It was really a mixed bag, but regardless, there is always room to optimize the Linux virtualization performance in a multi-threaded environment. This though could potentially be a greater issue as CPUs continue gaining more processing cores.

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Michael Larabel

Michael Larabel is the principal author of and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via