linux-kernel - Re: [PATCH 2/3] preempt/dynamic: Introduce preempt mode accessors

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Message-ID: <20220314200641.GV4285@paulmck-ThinkPad-P17-Gen-1>
Date:   Mon, 14 Mar 2022 13:06:41 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Marco Elver <elver@...gle.com>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Uladzislau Rezki <uladzislau.rezki@...y.com>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 2/3] preempt/dynamic: Introduce preempt mode accessors

On Mon, Mar 14, 2022 at 03:44:39PM +0100, Marco Elver wrote:
> On Mon, 14 Mar 2022 at 14:37, Frederic Weisbecker <frederic@...nel.org> wrote:
> >
> > From: Valentin Schneider <valentin.schneider@....com>
> >
> > CONFIG_PREEMPT{_NONE, _VOLUNTARY} designate either:
> > o The build-time preemption model when !PREEMPT_DYNAMIC
> > o The default boot-time preemption model when PREEMPT_DYNAMIC
> >
> > IOW, using those on PREEMPT_DYNAMIC kernels is meaningless - the actual
> > model could have been set to something else by the "preempt=foo" cmdline
> > parameter.
> >
> > Introduce a set of helpers to determine the actual preemption mode used by
> > the live kernel.
> >
> > Suggested-by: Marco Elver <elver@...gle.com>
> > Signed-off-by: Valentin Schneider <valentin.schneider@....com>
> > Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> > Cc: Uladzislau Rezki <uladzislau.rezki@...y.com>
> > Cc: Joel Fernandes <joel@...lfernandes.org>
> > Cc: Boqun Feng <boqun.feng@...il.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Neeraj Upadhyay <quic_neeraju@...cinc.com>
> > ---
> >  include/linux/sched.h | 16 ++++++++++++++++
> >  kernel/sched/core.c   | 11 +++++++++++
> >  2 files changed, 27 insertions(+)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 508b91d57470..d348e886e4d0 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -2096,6 +2096,22 @@ static inline void cond_resched_rcu(void)
> >  #endif
> >  }
> >
> > +#ifdef CONFIG_PREEMPT_DYNAMIC
> > +
> > +extern bool preempt_mode_none(void);
> > +extern bool preempt_mode_voluntary(void);
> > +extern bool preempt_mode_full(void);
> > +
> > +#else
> > +
> > +#define preempt_mode_none() IS_ENABLED(CONFIG_PREEMPT_NONE)
> > +#define preempt_mode_voluntary() IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY)
> > +#define preempt_mode_full() IS_ENABLED(CONFIG_PREEMPT)
> > +
> 
> Shame this was somehow forgotten.
> There was a v3 of this patch that fixed a bunch of things (e.g. making
> these proper functions so all builds error if accidentally used in
> #if).
> 
> https://lore.kernel.org/lkml/20211112185203.280040-3-valentin.schneider@arm.com/
> 
> Is it also possible to take all the rest of that series (all 4
> patches) from Valentin?

Me, I am assuming that #2/3 is an experimental test so that I am able
to easily whack this series over the head with rcutorture.  ;-)

							Thanx, Paul