linux-kernel - Re: [ckrm-tech] [RFC] Resource Management

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Message-Id: <20061030030635.98563962.pj@sgi.com>
Date:	Mon, 30 Oct 2006 03:06:35 -0800
From:	Paul Jackson <pj@....com>
To:	"Paul Menage" <menage@...gle.com>
Cc:	vatsa@...ibm.com, dev@...nvz.org, sekharan@...ibm.com,
	ckrm-tech@...ts.sourceforge.net, balbir@...ibm.com,
	haveblue@...ibm.com, linux-kernel@...r.kernel.org,
	matthltc@...ibm.com, dipankar@...ibm.com, rohitseth@...gle.com
Subject: Re: [ckrm-tech] [RFC] Resource Management - Infrastructure choices

Paul M wrote:
> The cpusets code which this was based on simply locked the task list,
> and traversed it to find threads in the cpuset of interest; you could
> do the same thing in any other resource controller.

I get away with this in the cpuset code because:
 1) I have the cpuset pointer directly in 'task_struct', so don't
    have to chase down anything, for each task, while scanning the
    task list.  I just have to ask, for each task, if its cpuset
    pointer points to the cpuset of interest.
 2) I don't care if I get an inconsistent answer, so I don't have
    to lock each task, nor do I even lockout the rest of the cpuset
    code.  All I know, at the end of the scan, is that each task that
    I claim is attached to the cpuset in question was attached to it at
    some point during my scan, not necessarilly all at the same time.
 3) It's not a flaming disaster if the kmalloc() of enough memory
    to hold all the pids I collect in a single array fails.  That
    just means that some hapless users open for read of a cpuset
    'tasks' file failed, -ENOMEM.  Oh well ...

If someone is actually trying to manage system resources accurately,
they probably can't get away being as fast and loose as this.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.925.600.0401
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