linux-kernel - Re: [PATCH documentation 1/2] nohz1: Add documentation.

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Message-ID: <51684AD3.7090305@linux.intel.com>
Date:	Fri, 12 Apr 2013 10:56:35 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu, Kevin Hilman <khilman@...aro.org>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH documentation 1/2] nohz1: Add documentation.


> ------------------------------------------------------------------------
>
> 1.	It increases the number of instructions executed on the path
> 	to and from the idle loop.
>
> 2.	On many architectures, dyntick-idle mode also increases the
> 	number of times that clocks must be reprogrammed, and this
> 	reprogramming can be quite expensive.


it's really that we're no longer using periodic clocks, but only one-shot clocks only.
(which then leads to having to program them every time)

but arguably, that's because of HRTIMERS more than NOHZ
(e.g. I bet we still turn off periodic even for nohz as long as hrtimers are enabled)

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