linux-kernel - Re: [PATCH 00/30] PREEMPT_AUTO: support lazy rescheduling

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Date: Wed, 14 Feb 2024 19:45:18 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Ankur Arora <ankur.a.arora@...cle.com>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de, peterz@...radead.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
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	David.Laight@...lab.com, richard@....at, jon.grimm@....com,
	bharata@....com, boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Subject: Re: [PATCH 00/30] PREEMPT_AUTO: support lazy rescheduling

On Wed, Feb 14, 2024 at 06:03:28PM -0800, Ankur Arora wrote:
> 
> Paul E. McKenney <paulmck@...nel.org> writes:
> 
> > On Mon, Feb 12, 2024 at 09:55:24PM -0800, Ankur Arora wrote:
> >> Hi,
> >>
> >> This series adds a new scheduling model PREEMPT_AUTO, which like
> >> PREEMPT_DYNAMIC allows dynamic switching between a none/voluntary/full
> >> preemption model. However, unlike PREEMPT_DYNAMIC, it doesn't depend
> >> on explicit preemption points for the voluntary models.
> >>
> >> The series is based on Thomas' original proposal which he outlined
> >> in [1], [2] and in his PoC [3].
> >>
> >> An earlier RFC version is at [4].
> >
> > This uncovered a couple of latent bugs in RCU due to its having been
> > a good long time since anyone built a !SMP preemptible kernel with
> > non-preemptible RCU.  I have a couple of fixes queued on -rcu [1], most
> > likely for the merge window after next, but let me know if you need
> > them sooner.
> 
> Thanks. As you can probably tell, I skipped out on !SMP in my testing.
> But, the attached diff should tide me over until the fixes are in.

That was indeed my guess.  ;-)

> > I am also seeing OOM conditions during rcutorture testing of callback
> > flooding, but I am still looking into this.
> 
> That's on the PREEMPT_AUTO && PREEMPT_VOLUNTARY configuration?

On two of the PREEMPT_AUTO && PREEMPT_NONE configurations, but only on
two of them thus far.  I am running a longer test to see if this might
be just luck.  If not, I look to see what rcutorture scenarios TREE10
and TRACE01 have in common.

							Thanx, Paul