A Last Minute Fix For EEVDF Scheduling Lag With Linux 6.13

Ahead of the Linux 6.13 stable kernel expected to be released later today, there is a last minute fix for the EEVDF CPU scheduler.

Sent out a few minutes ago was sched/urgent for v6.13. Of the two patches making it into the urgent queue ahead of Linux 6.13 stable is a fix to avoid scheduling lag. The fix is to compute lag properly to avoid an EEVDF entity placement issue.

Intel Linux engineer Peter Zijlstra discovered earlier this month this EEVDF entity placement bug causing scheduling lag. Peter ended up discovering "the trace shows it is all off" and when checking out the code discovering "all sorts of broken."

The patch being merged is described as: "isn't perfect yet, but much closer."

The 145 line rework to helping to avoid this scheduling lag in Linux 6.13 can be found via the sched pull request that should be merged to the mainline kernel in the coming hours. This is a fix to an EEVDF scheduler patch from November 2023, so presumably this fix will also be back-ported to existing stable kernels of the past year.