linux-kernel - Re: [PATCH] nohz: Prevent broadcast source from stealing full dynticks timekeeping duty

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Date:	Thu, 30 May 2013 15:57:17 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, Jiri Bohac <jbohac@...e.cz>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] nohz: Prevent broadcast source from stealing full dynticks
 timekeeping duty

On Wed, 29 May 2013, Frederic Weisbecker wrote:

> The timekeeping duty is currently assigned to the CPU that
> handles the tick broadcast clock device by the time it is set in
> one shot mode.
> 
> The reason for this is not entirely clear as outlined by Jiri
> Bohac: https://patchwork.kernel.org/patch/2302951/
> 
> One could speculate though that it makes sure only one CPU
> is woken up to fixup the timekeeping max deferment. But the
> timekeeper can change anytime after the broadcast CPU becomes
> idle. So probably we can remove this as in Jiri's patch, but
> not late in the -rc's.

Looking at commit 7300711e (clockevents: broadcast fixup possible
waiters) which introduced that takeover, I really can't see a reason
why we must do that. It's safe to remove it completely even now.

Thanks,

	tglx




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