Linux RCU subsystem development
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From: Ankur Arora <ankur.a.arora@oracle.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ankur Arora <ankur.a.arora@oracle.com>,
	paulmck@kernel.org, linux-kernel@vger.kernel.org,
	peterz@infradead.org, torvalds@linux-foundation.org,
	akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de,
	dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com,
	juri.lelli@redhat.com, vincent.guittot@linaro.org,
	willy@infradead.org, mgorman@suse.de, jpoimboe@kernel.org,
	mark.rutland@arm.com, jgross@suse.com, andrew.cooper3@citrix.com,
	bristot@kernel.org, mathieu.desnoyers@efficios.com,
	geert@linux-m68k.org, glaubitz@physik.fu-berlin.de,
	anton.ivanov@cambridgegreys.com, mattst88@gmail.com,
	krypton@ulrich-teichert.org, rostedt@goodmis.org,
	David.Laight@aculab.com, richard@nod.at, mjguzik@gmail.com,
	jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com,
	boris.ostrovsky@oracle.com, konrad.wilk@oracle.com,
	rcu@vger.kernel.org
Subject: Re: [PATCH 15/30] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y
Date: Mon, 11 Mar 2024 20:16:12 -0700	[thread overview]
Message-ID: <87msr4f8cj.fsf@oracle.com> (raw)
In-Reply-To: <5b78a338-cb82-4ac4-8004-77a3eb150604@joelfernandes.org>


Joel Fernandes <joel@joelfernandes.org> writes:

> Hi, Thomas,
> Thanks for your reply! I replied below.
>
> On 3/11/2024 3:12 PM, Thomas Gleixner wrote:
>> On Mon, Mar 11 2024 at 11:25, Joel Fernandes wrote:

   [ ... ]

>> What's wrong with the combination of PREEMPT_AUTO=y and PREEMPT_RCU=n?
>> Paul and me agreed long ago that this needs to be supported.
>
> There's nothing wrong with it. Its just a bit quirky (again just a point of
> view), that for a configuration that causes preemption (similar to
> CONFIG_PREEMPT=y), that PREEMPT_RCU can be disabled. After all, again with
> CONFIG_PREEMPT=y, PREEMPT_RCU cannot be currently disabled.

I think the argument was that PREEMPT_RCU=y is suboptimal for certain
workloads, and those configurations might prefer the stronger
forward-progress guarantees that PREEMPT_RCU=n provides.

See this:
https://lore.kernel.org/lkml/73ecce1c-d321-4579-b892-13b1e0a0620a@paulmck-laptop/T/#m6aab5a6fd5f1fd4c3dc9282ce564e64f2fa6cdc3

and the surrounding thread.

Thanks

--
ankur

  reply	other threads:[~2024-03-12  3:17 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20240213055554.1802415-1-ankur.a.arora@oracle.com>
     [not found] ` <20240213055554.1802415-16-ankur.a.arora@oracle.com>
2024-03-10 10:03   ` [PATCH 15/30] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y Joel Fernandes
2024-03-10 18:56     ` Paul E. McKenney
2024-03-11  0:48       ` Joel Fernandes
2024-03-11  3:56         ` Paul E. McKenney
2024-03-11 15:01           ` Joel Fernandes
2024-03-11 20:51             ` Ankur Arora
2024-03-11 22:12               ` Thomas Gleixner
2024-03-11  5:18         ` Ankur Arora
2024-03-11 15:25           ` Joel Fernandes
2024-03-11 19:12             ` Thomas Gleixner
2024-03-11 19:53               ` Paul E. McKenney
2024-03-11 20:29                 ` Thomas Gleixner
2024-03-12  0:01                   ` Paul E. McKenney
2024-03-12  0:08               ` Joel Fernandes
2024-03-12  3:16                 ` Ankur Arora [this message]
2024-03-12  3:24                   ` Joel Fernandes
2024-03-12  5:23                     ` Ankur Arora

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