linux-kernel - Re: [ckrm-tech] [PATCH 3/9] Containers (V9): Add tasks file interface

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Message-ID: <20070502032541.GA7311@in.ibm.com>
Date:	Wed, 2 May 2007 08:55:41 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	"Paul Menage" <menage@...gle.com>
Cc:	balbir@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	ckrm-tech@...ts.sourceforge.net, balbir@...ibm.com,
	haveblue@...ibm.com, xemul@...ru, dev@...ru, rohitseth@...gle.com,
	pj@....com, ebiederm@...ssion.com, mbligh@...gle.com,
	containers@...ts.osdl.org, serue@...ibm.com,
	akpm@...ux-foundation.org, svaidy@...ux.vnet.ibm.com,
	devel@...nvz.org
Subject: Re: [ckrm-tech] [PATCH 3/9] Containers (V9): Add tasks file interface

On Tue, May 01, 2007 at 01:37:24PM -0700, Paul Menage wrote:
> > Any chance we could get a per-container task list? It will
> > help subsystem writers as well.
> 
> It would be possible, yes - but we probably wouldn't want the overhead
> (additional ref counts and list manipulations on every fork/exit) of
> it on by default. We could make it a config option that particular
> subsystems could select.
> 
> I guess the question is how useful is this really, compared to just
> doing a do_each_thread() and seeing which tasks are in the container?
> Certainly that's a non-trivial operation, but in what circumstances is
> it really necessary to do it?

For the CPU controller I was working on, (a fast access to) such a list would 
have been valuable. Basically each task has a weight associated with it
(p->load_weight) which is made to depend upon its class limit. Whenever
the class limit changes, we need to go and change all its member task's 
->load_weight value. 

If you don't maintain the per-container task list, I guess I could still
work around it, by either:

	- Walk the task table and find relevant members, OR better
	  perhaps
	- Move p->load_weight to a class structure

-- 
Regards,
vatsa
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