linux-kernel - Re: boot cgroup questions

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Message-ID: <47FE4D4A.70109@qualcomm.com>
Date:	Thu, 10 Apr 2008 10:24:26 -0700
From:	Max Krasnyanskiy <maxk@...lcomm.com>
To:	Paul Jackson <pj@....com>
CC:	menage@...gle.com, mingo@...e.hu, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org
Subject: Re: boot cgroup questions

Sorry for disappearing on you guys. I'm working on releasing the user-space 
framework and engine that uses cpu isolation for hard-RT. Once that's done I'm 
going to resurrect these efforts. In the mean time let me reply to your last 
comments.

Paul Jackson wrote:
>> How about we add support for sym links to the cgroup fs ?
> 
> Still pollutes the primary cpuset name space ... you have all
> the directories X, X/A, and X/B as well as the symlinks A and B.
> 
> Symlinks allow for one path that needs to be 'aliased' to another,
> but they are a one-way map; without an exhaustive search of the
> potential namespace, one can't invert them, or determine if they
> can't be inverted.
> 
> Tools have to constantly make heuristic decisions whether to
> default to dereferencing the symlink, or not, and often have to
> provide alternatives for the non-default choice.
> 
> They are a pain in the backside even if designed in and expected
> up front.
> 
> If added as critical structure after the fact, something breaks,
> pretty much for sure.
> 
> For one minor example, code I've probably buried someplace that
> does "find /dev/cpuset -type d" to find all cpusets would break.
> 
> Or the one-line /sbin/cpuset_release_agent script:
> 	rmdir /dev/cpuset/$1
> is broken -- fails to clean-up associated symlinks, and can't
> avoid race conditions if it tries to add code to do that.
> 
>> Crazy idea.
> 
> Agreed ;)

Got it. Symlinks are out :)

Max


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