linux-kernel - Re: [RFC PATCH 47/86] rcu: select PREEMPT

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Message-ID: <106ab2d8-f63b-4c52-a93f-fc499d43fc13@paulmck-laptop>
Date:   Tue, 5 Dec 2023 20:07:49 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        torvalds@...ux-foundation.org, linux-mm@...ck.org, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        willy@...radead.org, mgorman@...e.de, jon.grimm@....com,
        bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com, mingo@...nel.org,
        bristot@...nel.org, mathieu.desnoyers@...icios.com,
        geert@...ux-m68k.org, glaubitz@...sik.fu-berlin.de,
        anton.ivanov@...bridgegreys.com, mattst88@...il.com,
        krypton@...ich-teichert.org, David.Laight@...lab.com,
        richard@....at, mjguzik@...il.com,
        Simon Horman <horms@...ge.net.au>,
        Julian Anastasov <ja@....bg>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [RFC PATCH 47/86] rcu: select PREEMPT_RCU if PREEMPT

On Tue, Dec 05, 2023 at 12:18:26PM -0800, Ankur Arora wrote:
> 
> Paul E. McKenney <paulmck@...nel.org> writes:
> 
> > On Tue, Dec 05, 2023 at 10:01:14AM -0500, Steven Rostedt wrote:
> >> On Mon, 4 Dec 2023 17:01:21 -0800
> >> "Paul E. McKenney" <paulmck@...nel.org> wrote:
> >>
> >> > On Tue, Nov 28, 2023 at 11:53:19AM +0100, Thomas Gleixner wrote:
> >> > > Paul!
> >> > >
> >> > > On Tue, Nov 21 2023 at 07:19, Paul E. McKenney wrote:
> >> > > > On Tue, Nov 21, 2023 at 10:00:59AM -0500, Steven Rostedt wrote:
> ...
> >> > >   3) Looking at the initial problem Ankur was trying to solve there is
> >> > >      absolutely no acceptable solution to solve that unless you think
> >> > >      that the semantically invers 'allow_preempt()/disallow_preempt()'
> >> > >      is anywhere near acceptable.
> >> >
> >> > I am not arguing for allow_preempt()/disallow_preempt(), so for that
> >> > argument, you need to find someone else to argue with.  ;-)
> >>
> >> Anyway, there's still a long path before cond_resched() can be removed. It
> >> was a mistake by Ankur to add those removals this early (and he has
> >> acknowledged that mistake).
> >
> > OK, that I can live with.  But that seems to be a bit different of a
> > take than that of some earlier emails in this thread.  ;-)
> 
> Heh I think it's just that this thread goes to (far) too many places :).
> 
> As Steven says, the initial series touching everything all together
> was a mistake. V1 adds the new preemption model alongside the existing
> ones locally defines cond_resched() as nop.
> 
> That'll allow us to experiment and figure out where there are latency
> gaps.

Sounds very good!

Again, I am very supportive of the overall direction.  Devils and details
and all that.  ;-)

							Thanx, Paul