linux-kernel - Re: [PATCH 02/32 RESEND] nohz: Drop ts->idle

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Message-ID: <1314627792.2816.60.camel@twins>
Date:	Mon, 29 Aug 2011 16:23:12 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Avi Kivity <avi@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Menage <menage@...gle.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: Re: [PATCH 02/32 RESEND] nohz: Drop ts->idle_active

On Mon, 2011-08-15 at 17:51 +0200, Frederic Weisbecker wrote:
> ts->idle_active is used to know if we want to account the idle sleep
> time. But ts->inidle is enough to check that.
> 
While possibly true, its not immediately obvious and no hints are
supplied. For example: tick_check_nohz() would disable ->idle_active..
where is this mirrored in the ->inidle state.

Also, tick_nohz_stop_sched_tick() has this comment:

	/*
	 * Set ts->inidle unconditionally. Even if the system did not
	 * switch to NOHZ mode the cpu frequency governers rely on the
	 * update of the idle time accounting in tick_nohz_start_idle().
	 */
	ts->inidle = 1;

Which suggest the ->inidle state doesn't accurately reflect things.

This is all rather hairy code, such changes really want more in terms of
explanation.


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