Date: Mon, 22 Nov 2010 11:52:42 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>,
        Mike Galbraith <efault@gmx.de>, Hans-Peter Jansen <hpj@urpla.net>,
        linux-kernel@vger.kernel.org,
        Lennart Poettering <mzxreary@0pointer.de>,
        Linus Torvalds <torvalds@linux-foundation.org>, david@lang.hm,
        Dhaval Giani <dhaval.giani@gmail.com>, Vivek Goyal <vgoyal@redhat.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Markus Trippelsdorf <markus@trippelsdorf.de>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Ingo Molnar <mingo@elte.hu>
Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups
Message-ID: <20101122062242.GE12043@balbir.in.ibm.com>
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* Peter Zijlstra <a.p.zijlstra@chello.nl> [2010-11-19 12:49:36]:

> On Fri, 2010-11-19 at 00:43 +0100, Samuel Thibault wrote:
> > What overhead? The implementation of cgroups is actually already
> > hierarchical. 
> 
> It must be nice to be that ignorant ;-) Speaking for the scheduler
> cgroup controller (that being the only one I actually know), most all
> the load-balance operations are O(n) in the number of active cgroups,
> and a lot of the cpu local schedule operations are O(d) where d is the
> depth of the cgroup tree.
>
> [ and that's with the .38 targeted code, current mainline is O(n ln(n))
> for load balancing and truly sucks on multi-socket ]
>

I can say that for memory, with hierarchies we account all the way up,
which can be a visible overhead, depending on how often you fault.
 

-- 
	Three Cheers,
	Balbir
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