KVM Changes For Linux 5.4 Fix Performance Regression, Add UMWAIT Support

Written by Michael Larabel in Virtualization on 29 September 2019 at 09:00 AM EDT. 3 Comments
A second batch of Kernel-based Virtual Machine (KVM) changes for the Linux 5.4 kernel have landed.

The first pull of KVM changes for Linux 5.4 last week weren't too exciting. That original pull brought support on ARM for up to 512 virtual CPUs, an ARM ITS translation cache, IPI x86 optimizations, and a wide variety of x86 bug fixes.

Sent out on Friday and since merged to mainline were a second batch of KVM changes arguably more interesting than the first:

- Improvements for nested virtualization.

- Restoring some performance optimizations that were accidentally removed in Linux 5.2.

- Support for the new Intel UMWAIT, UMONITOR, and TPAUSE instructions. UMWAIT is a power-savings feature coming initially with the "Tremont" cores and allows for a lightweight power/performance state.

- Support for informing Microsoft Windows guests if SMT is disabled by the host.

- Better detection of VMEXIT costs.

And the other assortment of fixes and improvements. The complete list can be found via the PR.
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Michael Larabel is the principal author of Phoronix.com 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 OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via MichaelLarabel.com.

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