Re: sched/fair: DELAY_DEQUEUE causes ~25% pipe IPC regression on Raspberry Pi 5

[Mike Galbraith]

On Tue, 2026-04-21 at 14:46 +0200, Tom Gebhardt wrote:
> 
> The fact that your local 6.12.y branch with patches 0047 and 0089
> (Christian's "Prevent negative lag increase during delayed dequeue")
> does not reproduce the issue is very encouraging. It suggests that the
> downstream RPi kernel just hasn't picked up those fixes yet, which
> explains why we still see the regression on stock rpi-6.12.y.

Not sure.  Taking stress-ng 0.15.06 to trusty ole x86_64 i4790 desktop
box, since I see no excuse for it to be arch specific, the virgin
6.12.82 DELAY_DEQUEUE delta for a pure voluntary config (lowest
overhead) was -6%.  Adding all eevdf backports took it to -3%.  To me
that looks very much like a nothing-burger, ie routine bench jitter
when diddling *anything* in fastpaths.

The only clear signal has come from that pi5 6.12.75+rpt-rpi-2712 plus
stress-ng 0.15.06 combo.


	-Mike