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

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Date:	Mon, 29 Aug 2011 16:23:10 +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 01/32 RESEND] nohz: Drop useless call in
 tick_nohz_start_idle()

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.

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?
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