Re: [PATCH] sched/fair: Add null pointer check to pick_next_entity()

Mike Galbraith
2025-04-19T02:53:26Z

On Fri, 2025-04-18 at 17:44 +0200, Peter Zijlstra wrote:
>
> However, due to PREEMPT_NONE, it is possible (Chris mentioned direct
> reclaim and OOM) to have very long (in-kernel) runtimes without
> scheduling.

Dunno what Chris considers 'very long', but FYI you can take some
pretty awful hits even sans PREEMPT_NONE. In 6.12 time frame I caught
move_expired_inodes() eating 66ms, and isolate_lru_folios() holding
IRQs off for 78ms via dirt simple kbuild+bonnie on spinning rust.

(fugly bandaids for both linger in my 6.12+ trees compost heaps)

> (I suppose this should be visible by tracing sched_switch)

(I used modified wakeup_rt that only traces max prio)

-Mike