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

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Message-ID: <20130701191949.GS3773@linux.vnet.ibm.com>
Date:	Mon, 1 Jul 2013 12:19:49 -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 06:19:10PM +0200, Andi Kleen wrote:
> > 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.
> 
> FWIW if you want useful testing you need to enable it by default
> (as part of NO_IDLE_HZ) anyways. Users will most likely pick
> whatever is "default" in Kconfig.

At this point in the process, I want testers who choose to test.  Hapless
victim testers come later.  Well, other than randconfig testers, but I
consider them to be voluntary hapless victims.  ;-)

> > > 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.
> 
> What performance part? 
> 
> Are you saying this adds so many checks to hot paths that normal runtime
> if() with a flag is too expensive?

I am saying that I don't know, and that I want to make it easy for people
to find out by comparing to the base configuration -- and for me to be
able to detect this from their .config file.

							Thanx, Paul

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