Re: [REGRESSION] sched/fair: Reimplement NEXT_BUDDY to align with EEVDF goals

[Peter Zijlstra]

On Fri, Jan 09, 2026 at 10:15:46AM +0000, Ryan Roberts wrote:

> Here are the updated results, now including column for "revert #1 & #2".
> 
> 6-18-0 (base)		(baseline)
> 6-19-0-rc1		(New NEXT_BUDDY implementation enabled)
> revert #1 & #2		(NEXT_BUDDY disabled)
> revert #2		(Old NEXT_BUDDY implementation enabled)
> 
> 
> The regressions that are fixed by "revert #2" (as originally reported) are still 
> fixed in "revert #1 & #2". Interestingly, performance actually improves further 
> for the latter in the multi-node mysql benchmark (which is our VIP workload). 
> There are a couple of hackbench cases (sockets with high thread counts) that 
> showed an improvement with "revert #2" but which is gone with "revert #1 & #2".
> 
> Let me know if I can usefully do anything else.

If its not too much bother, could you run 6.19-rc with SCHED_BATCH ? The
defining characteristic of BATCH is that it fully ignores wakeup
preemption.