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

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Message-ID: <87il5cpfn1.fsf@oracle.com>
Date:   Tue, 05 Dec 2023 12:18:26 -0800
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     paulmck@...nel.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ankur Arora <ankur.a.arora@...cle.com>,
        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 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.

Ankur