linux-kernel - Re: Does anyone use CONFIG_TINY_PREEMPT

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Message-ID: <CAFTL4hyHHRzgsAy6KbA39YgEjPRkMRdDK17DWy_rehiyoJjo6A@mail.gmail.com>
Date:	Tue, 13 Nov 2012 02:34:06 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org, mingo@...e.hu,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, sbw@....edu,
	patches@...aro.org
Subject: Re: Does anyone use CONFIG_TINY_PREEMPT_RCU?

2012/11/13 Josh Triplett <josh@...htriplett.org>:
> On Tue, Nov 13, 2012 at 02:12:27AM +0100, Frederic Weisbecker wrote:
>> 2012/11/13 Paul E. McKenney <paulmck@...ux.vnet.ibm.com>:
>> > Hello!
>> >
>> > I know of people using TINY_RCU, TREE_RCU, and TREE_PREEMPT_RCU, but I
>> > have not heard of anyone using TINY_PREEMPT_RCU for whom TREE_PREEMPT_RCU
>> > was not a viable option (in contrast, the people running Linux on
>> > tiny-memmory systems typically use TINY_RCU).  Of course, if no one
>> > really needs it, the proper thing to do is to remove it.
>> >
>> > So, if you need TINY_PREEMPT_RCU, please let me know.  Otherwise, I will
>> > remove it, probably in the 3.9 timeframe.
>>
>> I don't use it personally but if you remove it, does that mean that
>> RCU couldn't be preemptible on UP?
>
> No, it would mean that on UP you could choose between TINY_RCU and
> TREE_PREEMPT_RCU, depending on whether you want tiny or preemptible.

Ok. I thought the TREE version wasn't possible anymore on UP when I
saw some patches that removed optimizations for nr_online_cpus=1.
Hence the confusion.
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