Linux 5.11 Sees Quick Fix For A Context Switching Performance Regression
Written by Michael Larabel in Linux Kernel on 27 December 2020 at 07:35 AM EST. 2 Comments
LINUX KERNEL --
Linux 5.11-rc1 is due for release later today and at least one regression has seen a quick resolution.

Intel's kernel test robot saw a ~1.6% performance regression in one of its scheduler benchmarks. The change causing the regression was trying to ensure only per-CPU KThreads run during hotplug.

Thanks to that timely testing by Intel, There is a fix of optimizing the finish_lock_switch() function within the scheduler code. Kernel developer Peter Zijlstra noted, "Even though we were careful to replace a single load with another single load from the same cacheline. Restore finish_lock_switch() to the exact state before the offending patch and solve the problem differently."

That fix was sent in today ahead of the Linux 5.11-rc1 release. Great seeing one more performance regression resolved timely albeit a small one in this case.

As to the separate regression we've been looking at with AMD performance regressing on Linux 5.11 when using the common default "Schedutil" governor, I have some new data likely going up in a few hours once those tests complete looking at some different configurations.
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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 or contacted via MichaelLarabel.com.

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