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

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Message-ID: <20130412203904.GL29861@linux.vnet.ibm.com>
Date:	Fri, 12 Apr 2013 13:39:04 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Arjan van de Ven <arjan@...ux.intel.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.

On Fri, Apr 12, 2013 at 10:56:35AM -0700, Arjan van de Ven wrote:
> 
> >------------------------------------------------------------------------
> >
> >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)

Fair enough, but I believe that I have captured this.

> 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)

Might be, but the more detail I add, the higher the maintenance burden
keeping this document up to date.  ;-)

							Thanx, Paul

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