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

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Message-ID: <20130701161910.GN6123@two.firstfloor.org>
Date:	Mon, 1 Jul 2013 18:19:10 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Andi Kleen <andi@...stfloor.org>, 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

> 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.

> > 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?

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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