linux-kernel - Re: [RFC] cgroup TODOs

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Message-ID: <1347621302.7172.22.camel@twins>
Date:	Fri, 14 Sep 2012 13:15:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
	Michal Hocko <mhocko@...e.cz>,
	Glauber Costa <glommer@...allels.com>,
	Paul Turner <pjt@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Graf <tgraf@...g.ch>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Neil Horman <nhorman@...driver.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [RFC] cgroup TODOs

On Thu, 2012-09-13 at 13:58 -0700, Tejun Heo wrote:
>   The cpu ones handle nesting correctly - parent's accounting includes
>   children's, parent's configuration affects children's unless
>   explicitly overridden, and children's limits nest inside parent's. 

The implementation has some issues with fixed point math limitations on
deep hierarchies/large cpu count, but yes.

Doing soft-float/bignum just isn't going to be popular I guess ;-)

People also don't seem to understand that each extra cgroup carries a
cost and that nested cgroups are more expensive still, even if the
intermediate levels are mostly empty (libvirt is a good example of how
not to do things).

Anyway, I guess what I'm saying is that we need to work on the awareness
of cost associated with all this cgroup nonsense, people seem to think
its all good and free -- or not think at all, which, while depressing,
seem the more likely option.
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