From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: [patch] clockevents: Reinstate the per cpu tick skew
Date: Wed, 28 Dec 2011 14:32:06 +0100
Message-ID: <4EFB1A56.1040902@linux.intel.com>
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Cc: RT <linux-rt-users@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Ingo Molnar <mingo@elte.hu>
To: Mike Galbraith <efault@gmx.de>
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On 12/27/2011 10:20 AM, Mike Galbraith wrote:
> 
> Quoting removal commit af5ab277ded04bd9bc6b048c5a2f0e7d70ef0867 
> Historically, Linux has tried to make the regular timer tick on
> the various CPUs not happen at the same time, to avoid contention
> on xtime_lock.
> 
> Nowadays, with the tickless kernel, this contention no longer
> happens since time keeping and updating are done differently. In
> addition, this skew is actually hurting power consumption in a
> measurable way on many-core systems. End quote
> 
> Contention remains a problem if NO_HZ is either not configured, or
> is nohz=off disabled due to workload constraints.  The RT kernel
> running nohz=off was measured to be using > 1.4% CPU just ticking
> 64 CPUs, with tick perturbation reaching ~80us.  For loads where
> measured (>100us) NO_HZ latencies are intolerable, a must have.

I think we need to just say no to this, and kill the nohz=off option
entirely.

Seriously, are people still running with ticks for any legitimate
reasons? (and not just because they goofed their config file)
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