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Date: Thu, 9 Feb 2012 19:32:59 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Christoph Lameter <cl@linux.com>
Cc: Gilad Ben-Yossef <gilad@benyossef.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-kernel@vger.kernel.org,
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        Michal Nazarewicz <mina86@mina86.com>,
        Kosaki Motohiro <kosaki.motohiro@gmail.com>,
        Milton Miller <miltonm@bga.com>
Subject: Re: [v7 0/8] Reduce cross CPU IPI interference
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On Thu, Feb 09, 2012 at 10:26:02AM -0600, Christoph Lameter wrote:
> On Thu, 9 Feb 2012, Frederic Weisbecker wrote:
> 
> > > The vmstat timer only makes sense when the OS is doing something on the
> > > processor. Otherwise if no counters are incremented and the page and slab
> > > allocator caches are empty then there is no need to run the vmstat timer.
> >
> > So this is a typical example of a timer we want to shutdown when the CPU is idle
> > but we want to keep it running when we run in adaptive tickless mode (ie: shutdown
> > the tick while the CPU is busy).
> 
> You can also shut it down when the cpu is busy and not doing any system
> calls. If the percpu differentials are all zero (because you just ran the
> timer f.e.) and there are no system activities that would change the
> counters then there is no point in running the vmstat timer.

Yep. I believe we can probably find that timer pattern elsewhere as well.
A class of userspace/idle defferable timers.