linux-kernel - Re: [PATCH tip/core/rcu] Do not keep timekeeping CPU tick running for non-nohz

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Message-ID: <1406175844.5094.57.camel@marge.simpson.net>
Date:	Thu, 24 Jul 2014 06:24:04 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu] Do not keep timekeeping CPU tick running
 for non-nohz_full= CPUs

On Wed, 2014-07-23 at 18:02 +0200, Frederic Weisbecker wrote:

> Yes. Distros seem to want to make full dynticks available for users but they
> also want the off case (when nohz_full= isn't passed) to keep the lowest overhead
> as possible.

Yup, zero being the _desired_ number.  The general case can't afford any
fastpath cycles being added by a fringe feature, we're too fat now.

Imagines marketeer highlighting shiny new fringe feature: "...and most
network benchmarks show that we only lost a few percent throughput, so
you won't have to increase the size of your server farm _too_ much".

Ok, so my imagination conjured up a _stupid_ marketeer, you get it ;-)

-Mike

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