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Subject: Re: [PATCH 02/32 RESEND] nohz: Drop ts->idle_active
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Anton Blanchard <anton@au1.ibm.com>, Avi Kivity <avi@redhat.com>,
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        Stephen Hemminger <shemminger@vyatta.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tim Pepper <lnxninja@linux.vnet.ibm.com>
Date: Mon, 29 Aug 2011 16:23:12 +0200
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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.