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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <aY0HOKn1HuYn9efK@gpd4>
Date: Wed, 11 Feb 2026 23:48:24 +0100
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>
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

On Wed, Feb 11, 2026 at 12:37:13PM -1000, Tejun Heo wrote:
> 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()?

Nevermind, just ignore that comment, we clearly want to trigger
ops.dequeue/enqueue() in that case, it's the whole point of
SCX_DEQ_SCHED_CHANGE. I should probably go to bed and get some sleep. :)

-Andrea