linux-kernel - Re: nohz problem with idle time on old hardware

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Message-ID: <20140409113923.7dcaf183@gandalf.local.home>
Date:	Wed, 9 Apr 2014 11:39:23 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Matthew Whitehead <tedheadster@...il.com>,
	John Stultz <john.stultz@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	mwhitehe@...hat.com, Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: nohz problem with idle time on old hardware

On Wed, 9 Apr 2014 11:31:43 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> Hmm, looking at the code, I see it probably should still do the check.
> 
> OK, nevermind ;-)

Reading even more of the code, now I'm totally confused :-)

When tick_setup_sched_timer() is called, if tick_nohz_enabled is set,
then we set tick_nohz_active.

This gets called by hrtimer_switch_to_hres(), and before that is
called, the tick_check_oneshot_changed() will never get to the
tick_nohz_switch_to_nohz() call.

Looks to me, the real answer is to nuke both the if statement *and* the
setting of the tick_nohz_active in that function. Both looks a bit
redundant to me.

-- Steve
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