linux-kernel - Re: [PATCH RFC nohz_full 0/7] v2 Provide infrastructure for full-system idle

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Message-ID: <20130701160314.GM3773@linux.vnet.ibm.com>
Date:	Mon, 1 Jul 2013 09:03:14 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...icios.com, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	darren@...art.com, fweisbec@...il.com, sbw@....edu
Subject: Re: [PATCH RFC nohz_full 0/7] v2 Provide infrastructure for
 full-system idle

On Mon, Jul 01, 2013 at 08:19:25AM -0700, Andi Kleen wrote:
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> writes:
> >
> > The individual patches are as follows:
> >
> > 1.	Add a CONFIG_NO_HZ_FULL_SYSIDLE Kconfig parameter to enable
> > 	this feature.  Kernels built with CONFIG_NO_HZ_FULL_SYSIDLE=n
> > 	act exactly as they do today.
> 
> Is this extra CONFIG option really needed? RCU already has a bewildering
> variety of CONFIG options, and no idle CONFIG is also pretty complicated. 
> At some point noone will know how to configure kernels anymore if 
> these non trivial, complicated trade off CONFIGs keep spreading.
> 
> The facility sounds like a good thing in general. Just enable
> it implicitely with NO_HZ_SYSIDLE ? 

I am guessing that you want CONFIG_NO_HZ_FULL to implicitly enable
the sysidle code so that CONFIG_NO_HZ_FULL_SYSIDLE can be eliminated.
I will be happy to take that step, but only after I gain full confidence
in the correctness and performance of the sysidle code.

> If you want a switch for testing I would advise a sysctl or sysfs knob

This would work well for the correctness part, but not for the performance
part.

							Thanx, Paul

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