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

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Message-ID: <aY0EmUnmo4gGitcW@slm.duckdns.org>
Date: Wed, 11 Feb 2026 12:37:13 -1000
From: Tejun Heo <tj@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	Kuba Piecuch <jpiecuch@...gle.com>,
	Emil Tsalapatis <emil@...alapatis.com>,
	Christian Loehle <christian.loehle@....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,

On Wed, Feb 11, 2026 at 11:34:54PM +0100, Andrea Righi wrote:
> > The end result is about the same because whenever we migrate we're sending
> > it to the local DSQ of the destination CPU, so whether we generate the event
> > on deactivation of the source CPU or activation on the destination doesn't
> > make *whole* lot of difference. However, conceptually, migrations are
> > internal events. There isn't anything actionable for the BPF scheduler. The
> > reason why ops.dequeue() should be emitted is not because the task is
> > changing CPUs (which caused the deactivation) but the fact that it ends up
> > in a local DSQ afterwards. I think it'll be cleaner both conceptually and
> > code-wise to emit ops.dequeue() only from dispatch_enqueue() and dequeue
> > paths.
> 
> Does this include core scheduler migrations or just SCX-initiated
> migrations (move_remote_task_to_local_dsq())?
> 
> Because with core scheduler migrations we trigger ops.enqueue(), so we
> should also trigger ops.dequeue(). Or we need to send the task straight to
> local to prevent calling ops.enqueue().

I'm a bit lost. Can you elaborate on core scheduler migrations triggering
ops.enqueue()?

Thanks.

-- 
tejun