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

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Message-ID: <20231107192703.1c493431@gandalf.local.home>
Date:   Tue, 7 Nov 2023 19:27:03 -0500
From:   Steven Rostedt <rostedt@...dmis.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,
        paulmck@...nel.org, linux-mm@...ck.org, x86@...nel.org,
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        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
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        bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
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        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,  7 Nov 2023 13:57:33 -0800
Ankur Arora <ankur.a.arora@...cle.com> wrote:

> With PREEMPTION being always-on, some configurations might prefer
> the stronger forward-progress guarantees provided by PREEMPT_RCU=n
> as compared to PREEMPT_RCU=y.
> 
> So, select PREEMPT_RCU=n for PREEMPT_VOLUNTARY and PREEMPT_NONE and
> enabling PREEMPT_RCU=y for PREEMPT or PREEMPT_RT.
> 
> Note that the preemption model can be changed at runtime (modulo
> configurations with ARCH_NO_PREEMPT), but the RCU configuration
> is statically compiled.

I wonder if we should make this a separate patch, and allow PREEMPT_RCU=n
when PREEMPT=y?

This could allow us to test this without this having to be part of this
series.

-- Steve