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Message-ID: <1347621302.7172.22.camel@twins>
Subject: Re: [RFC] cgroup TODOs
From: Peter Zijlstra <peterz@infradead.org>
To: Tejun Heo <tj@kernel.org>
Cc: containers@lists.linux-foundation.org, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, Li Zefan <lizefan@huawei.com>,
        Michal Hocko <mhocko@suse.cz>, Glauber Costa <glommer@parallels.com>,
        Paul Turner <pjt@google.com>, Johannes Weiner <hannes@cmpxchg.org>,
        Thomas Graf <tgraf@suug.ch>, "Serge E. Hallyn" <serue@us.ibm.com>,
        Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Neil Horman <nhorman@tuxdriver.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Date: Fri, 14 Sep 2012 13:15:02 +0200
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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.