linux-kernel - Re: [RFC/PATCH -v2] Add sysfs control to modify a user's cpu share

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Date:	Thu, 04 Oct 2007 17:32:17 -0400
From:	Valdis.Kletnieks@...edu
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	lkml <linux-kernel@...r.kernel.org>, maneesh@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>
Subject: Re: [RFC/PATCH -v2] Add sysfs control to modify a user's cpu share

On Thu, 04 Oct 2007 10:54:51 +0200, Heiko Carstens said:
> >   echo 2048 > /sys/kernel/uids/500/cpu_share
> > 
> > this should just work too, regardless of there not being any UID 500 
> > tasks yet. Likewise, once configured, the /sys/kernel/uids/* directories 
> > (with the settings in them) should probably not go away either.
> 
> Shouldn't that be done via uevents? E.g. UID x gets added to the sysfs tree,
> generates a uevent and a script then figures out the cpu_share and sets it.

That would tend to be a tad racy - a site may want to set limits in the
hypothetical /sys/kernel/uids/NNN before the program has a chance to fork-bomb
or otherwise make it difficult to set a limitfrom within another userspace
process.  It's similar to why you want a process to be launched with all its
ulimit's set, rather than set them after the fork/exec happens...


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