Re: [PATCH v2] [tip: sched/core] sched: Move PLACE_LAG and RUN_TO_PARITY to sysctl

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Tue, Feb 11, 2025 at 11:36:44PM -0600, Cristian Prundeanu wrote:
> Replacing CFS with the EEVDF scheduler in kernel 6.6 introduced
> significant performance degradation in multiple database-oriented
> workloads. This degradation manifests in all kernel versions using EEVDF,
> across multiple Linux distributions, hardware architectures (x86_64,
> aarm64, amd64), and CPU generations.
> 
> Testing combinations of available scheduler features showed that the
> largest improvement (short of disabling all EEVDF features) came from
> disabling both PLACE_LAG and RUN_TO_PARITY.
> 
> Moving PLACE_LAG and RUN_TO_PARITY to sysctl will allow users to override
> their default values and persist them with established mechanisms.

Nope -- you have knobs in debugfs, and that's where they'll stay. Esp.
PLACE_LAG is super dodgy and should not get elevated to anything
remotely official.

Also, FYI, by keeping these emails threaded in the old thread I nearly
missed them again. I'm not sure where this nonsense of keeping
everything in one thread came from, but it is bloody stupid.