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

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Message-ID: <87sf4en6el.fsf@oracle.com>
Date:   Wed, 06 Dec 2023 17:33:06 -0800
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     paulmck@...nel.org
Cc:     Ankur Arora <ankur.a.arora@...cle.com>,
        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


Paul E. McKenney <paulmck@...nel.org> writes:

> 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.  ;-)

Agreed. And thanks!

--
ankur