linux-kernel - Re: Kconfig doesn't support select on choices (was Re: [GIT PULL] nohz: Adaptively stop the tick, finally)

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Message-ID: <CAFTL4hwBnU7ho=ihdruwkN+K-xra2QbQbRRGx-vEMtTcFGYwXA@mail.gmail.com>
Date:	Thu, 25 Apr 2013 15:46:55 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Michal Marek <mmarek@...e.cz>, LKML <linux-kernel@...r.kernel.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Kevin Hilman <khilman@...aro.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: Kconfig doesn't support select on choices (was Re: [GIT PULL]
 nohz: Adaptively stop the tick, finally)

2013/4/25 Ingo Molnar <mingo@...nel.org>:
>
> * Frederic Weisbecker <fweisbec@...il.com> wrote:
>
>> 2013/4/25 Ingo Molnar <mingo@...nel.org>:
>> >
>> > * Frederic Weisbecker <fweisbec@...il.com> wrote:
>> >
>> >> >         depends on VIRT_CPU_ACCOUNTING_GEN
>> >> >
>> >> > It should _really_ select both the RCU and the CPU time accounting model
>> >> > automatically!
>> >>
>> >> Yeah I know. I have yet to fix that in Kconfig (it's a Kconfig limitation).
>> >
>> > Why cannot we simply select it and its dependencies, explicitly, for the
>> > time being? Something like:
>> >
>> >         depends on 64BIT
>> >         select VIRT_CPU_ACCOUNTING
>> >         select VIRT_CPU_ACCOUNTING_GEN
>> >
>> > 90% of the .config's have VIRT_CPU_ACCOUNTING_GEN turned off, because it's
>> > a default-off feature - so dynticks-full is effectively hidden from the
>> > large majority of testers...
>>
>> Whatever we do, it seems that select does not work with choices.
>>
>> Michal, we are running into an issue where a Kconfig option needs to
>> select CONFIG_VIRT_CPU_ACCOUNTING_GEN but this latter option is part of
>> a choice menu so it doesn't work. As a result we are forced to use a
>> "depends on" and this hides the high level option we are interested in
>> (here full dynticks) behind its low level dependency. How hard do you
>> think it would be to fix this? I tried something that worked half-way
>> but I quickly got lost in the Kconfig maze.
>
> While it's not an ideal solution, we could try to create three bools out
> of the choice options, as a workaround?

I thought about that yeah, at least for a temporary solution. Let's
try it, I'll see what I can get.
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