RE: [PATCH v5] sched/fair: Add fair placement lag

[wangtao <tao.wangtao@honor.com>]

Hi,

Just a gentle ping on the patch I sent about two weeks ago.

  https://lore.kernel.org/all/20251222095700.6598-1-tao.wangtao@honor.com/

The patch targets question (2) in Section 4 "Fairness in Dynamic Systems"
of the EEVDF paper:

  "When a client with non-zero lag leaves the competition,
   what should be its lag when it rejoins the competition?"

Section 5 of the paper notes that there is no single clearly fair way
to handle this, and therefore presents three implementation strategies
(Strategy #1, #2, and #3) with different trade-offs. The current Linux
EEVDF implementation corresponds to Strategy #1.

The patch introduces FAIR_PLACE_LAG, which keeps V + J invariant
when there are runnable tasks, and aims to avoid the "V moving
backwards" and order-instability issues in the T1/T2/T3 example,
providing more stable and arguably fairer behavior when entities
frequently leave and rejoin. Hackbench results in the commit message
show some improvements.

Could you please take a look and let me know whether the overall
direction looks acceptable, and if exposing FAIR_PLACE_LAG as an
optional alternative to the existing Strategy #1 would be reasonable?
I'm happy to rework and send a new version if needed.

Thanks for your time.

Best regards,
Tao