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Subject: Re: [PATCH v2 14/14] Change CPUACCT to default n
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Turner <pjt@google.com>, Glauber Costa <glommer@parallels.com>,
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        daniel.lezcano@free.fr, jbottomley@parallels.com, fweisbec@gmail.com,
        Balbir Singh <bsingharora@gmail.com>
Date: Fri, 25 Nov 2011 11:09:49 +0100
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On Fri, 2011-11-25 at 10:05 +0800, Li Zefan wrote:
> > despite it being a not entirely natural fit.  Something I proposed at
> > Prague and that we could explore here is the idea of a co-mounted
> > controller.  In this example it would only be mountable with cpu so
> > you could always depend on the cpu hierarchy being there; likewise we
> > can put (jump-labeled) touchpoints within the cpu-subsystem to call
> > out for updates as appropriate when the co-mount exists.
> > 
> 
> IIUC, this co-mounting idea is something I implemented years ago:
> 
> https://lkml.org/lkml/2008/6/18/389
> 
> The use case and the reason it was rejected:
> 
> https://lkml.org/lkml/2008/7/1/97

"This allows one subsystem to require that it only be mounted when some
other subsystems are also present in the proposed hierarchy."

That's not exactly what I meant, what I meant was that say you co-mount
cpu,cpuset the combined mount provides more features/better performance
than if you don't. Which then provides a natural incentive to actually
co-mount the stuff.

You patch looks like it forces the co-mount.