EEVDF Scheduler Merged For Linux 6.6, Intel Hybrid Cluster Scheduling Re-Introduced

The EEVDF scheduler code has been merged for the in-development Linux 6.6 kernel. EEVDF replaces the existing CFS scheduler code. There is the likelihood of some performance regressions initially though but the developers will be working to address them as they arise. Additionally, this scheduler pull also re-introduces cluster scheduling for Intel Core hybrid processors.

EEVDF is ready to go in Linux 6.6 as a replacement to the existing CFS code. EEVDF is short for the Earliest Eligible Virtual Deadline First and is based on a research paper from the late 90's. This should result in better scheduling policy for the kernel while also exposing less knobs than CFS due to having better behavior.

We've been expecting EEVDF to land while on Monday, Linus Torvalds indeed went ahead and merged the code without any objections. It will be fun to benchmark EEVDF's impact with Linux 6.6.

The merge does mention the possibility of regressions:

" In terms of expected performance regressions: we will and can fix everything where a 'good' workload misbehaves with the new scheduler, but EEVDF inevitably changes workload scheduling in a binary fashion, hopefully for the better in the overwhelming majority of cases, but in some cases it won't, especially in adversarial loads that got lucky with the previous code, such as some variants of hackbench. We are trying hard to err on the side of fixing all performance regressions, but we expect some inevitable post-release iterations of that process."

The scheduler updates for Linux 6.6 also bring back cluster scheduling for Intel Core hybrid CPUs after the earlier code was found to induce performance regressions.

Linux 6.6 kernel benchmarking will be kicking off at Phoronix once the merge window is past and should be interesting given all the changes expected this cycle.