Re: [PATCH v2 3/3] sched_ext: Allow scx_bpf_reenqueue_local() to be called from anywhere

[Tejun Heo <tj@kernel.org>]

Hello,

On Wed, Oct 29, 2025 at 11:45:46AM +0100, Peter Zijlstra wrote:
> On Mon, Oct 27, 2025 at 08:19:40AM -1000, Tejun Heo wrote:
> > The ops.cpu_acquire/release() callbacks are broken - they miss events under
> > multiple conditions and can't be fixed without adding global sched core hooks
> > that sched maintainers don't want.
> 
> I think I'll object to that statement just a wee bit. I think we can
> make it work -- just not with the things proposed earlier.

Sure, I'll massage it a bit before committing.

> Anyway, if you want to reduce the sched_ext interface and remove
> cpu_acquire/release entirely, this is fine too.
> 
> I might still do that wakeup_preempt() change if I can merge / replace
> the queue_mask RETRY_TASK logic -- I have vague memories the RT people
> also wanted something like this a while ago and it isn't that big of a
> change.

Yeah, being able to create some kind of interlocking from ttwu to pick_task
is something generally useful, I think, even if I don't use it right now.

> 6.23 is a long time, can't we throw this out quicker? This thing wasn't
> supposed to be an ABI after all. A 1 release cycle seems fine to me ;-)

We've been discussing about compat policy lately and I think what we landed
on was maintaining compatibility, when reasonably possible, over one LTS
release + a couple non-LTS releases, which comes out to ~1.5 to 2 years.
That seems to give most people enough sliding room while not choking us with
too much compat overhead. This is a bit more work but it is actually
surprisingly not that painful with all the BPF compat features, and seems to
hit a reasonable balance.

Thanks.

-- 
tejun