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: <20130425134101.GA16609@gmail.com>
Date:	Thu, 25 Apr 2013 15:41:01 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
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)


* 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?

Thanks,

	Ingo
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