linux-kernel - Re: [PATCH 1/2] sched_ext: Fix ops.dequeue() semantics

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Message-ID: <aVG_WZCq5QlRgrqK@slm.duckdns.org>
Date: Sun, 28 Dec 2025 13:38:01 -1000
From: Tejun Heo <tj@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	Emil Tsalapatis <emil@...alapatis.com>,
	Daniel Hodges <hodgesd@...a.com>, sched-ext@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] sched_ext: Fix ops.dequeue() semantics

Hello again, again.

On Sun, Dec 28, 2025 at 01:28:04PM -1000, Tejun Heo wrote:
...
> So, please ignore that part. That's non-sense. I still wonder whether we can
> create some interlocking between scx_bpf_dsq_insert() and ops.dequeue()
> without making hot path slower. I'll think more about it.

And we can't create an interlocking between scx_bpf_dsq_insert() and
ops.dequeue() without adding extra atomic operations in hot paths. The only
thing shared is task rq lock and dispatch path can't do that synchronously.
So, yeah, it looks like the best we can do is always letting the BPF sched
know and let it figure out locking and whether the task needs to be
dequeued from BPF side.

Thanks.

-- 
tejun