linux-kernel - Re: [PATCH 2/4] timer: relax tick stop in idle entry

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Message-ID: <20151116154046.3e40c2cb@icelake>
Date:	Mon, 16 Nov 2015 15:40:46 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	paulmck@...ux.vnet.ibm.com, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	John Stultz <john.stultz@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Len Brown <len.brown@...el.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Paul Turner <pjt@...gle.com>,
	Josh Triplett <josh@...htriplett.org>,
	jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH 2/4] timer: relax tick stop in idle entry

On Mon, 16 Nov 2015 15:32:38 -0800
Arjan van de Ven <arjan@...ux.intel.com> wrote:

> On 11/16/2015 3:28 PM, Paul E. McKenney wrote:
> 
> > Is this mostly an special-purpose embedded thing, or do you expect
> > distros to be enabling this?  If the former, I suggest
> > , but if distros are doing this for
> > general-purpose workloads, I instead suggest CONFIG_RCU_FAST_NO_HZ.
> 
> thermal overload happens a lot on small devices, but sadly also in
> big datacenters where it is not uncommon to underprovision cooling
> capacity by a bit (it's one of those "99% of the time you only need
> THIS much, the 1% you need 30% more" and that more is expensive or
> even impractical)

CONFIG_RCU_FAST_NO_HZ is more inline with idle injection in that both
are targeted energy efficiency.
Checking ubuntu and fedora, seems both have CONFIG_RCU_NOCB_CPU_ALL=y.
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