linux-kernel - Re: [PATCH 01/32 RESEND] nohz: Drop useless call in tick_nohz_start

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Message-ID: <20110829171020.GC9748@somewhere.redhat.com>
Date:	Mon, 29 Aug 2011 19:10:22 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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>,
	Stephen Hemminger <shemminger@...tta.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>,
	Paul Menage <paul@...lmenage.org>
Subject: Re: [PATCH 01/32 RESEND] nohz: Drop useless call in
 tick_nohz_start_idle()

On Mon, Aug 29, 2011 at 04:23:10PM +0200, Peter Zijlstra wrote:
> On Mon, 2011-08-15 at 17:51 +0200, Frederic Weisbecker wrote:
> > The call to update_ts_time_stats() there is useless. All
> > we need is to save the idle entry_time.
> > 
> > 
> Would have been clearer if you just said the call was a NOP. The whole
> second sentence distracts and confuses as its irrelevant to the change
> at hand.
> 
> If you want to expand you can explain that its a NOP because
> update_ts_time_stats() requires either ts->idle_active and/or
> @last_update_time and our callsite has neither.

Right, will fix the changelog.

> 
> Although this assumes its never called when ts->idle_active is already
> set, is this so (likely)? Do we want a WARN_ON_ONCE() testing that
> assumption?

Not sure. Looking at the ondemand cpufreq governor, it calls
get_cpu_idle_time_us() from an initcall.
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