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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>, tglx@linutronix.de,
	mingo@kernel.org, linux-kernel@vger.kernel.org,
	juri.lelli@redhat.com, vincent.guittot@linaro.org,
	dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
	mgorman@suse.de, vschneid@redhat.com, efault@gmx.de
Subject: Re: [PATCH 0/5] sched: Lazy preemption muck
Message-ID: <20241009062019.1FJYnQL1@linutronix.de>
References: <20241007074609.447006177@infradead.org>
 <20241008153232.YwZfzF0r@linutronix.de>
 <87wmihdh3u.fsf@oracle.com>
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In-Reply-To: <87wmihdh3u.fsf@oracle.com>

On 2024-10-08 21:40:05 [-0700], Ankur Arora wrote:
> > While comparing this vs what I have:
> > - need_resched()
> >   It checked both (tif_need_resched_lazy() || tif_need_resched()) while
> >   now it only looks at tif_need_resched().
> >   Also ensured that raw_irqentry_exit_cond_resched() does not trigger on
> >   lazy.
> >   I guess you can argue both ways what makes sense, just noting=E2=80=A6
>=20
> I think we want need_resched() to be only tif_need_resched(). That way
> preemption in lazy mode *only* happens at the user mode boundary.

There are places such as __clear_extent_bit() or select_collect() where
need_resched() is checked and if 0 they loop again. For these kind of
users it would probably make sense to allow them to preempt themself.
We could also add a new function which checks both and audit all users
and check what would make sense base on $criteria.

Sebastian