linux-kernel - Re: [RFC][PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack of an arbitrary thread.

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Date:	Thu, 25 Jun 2015 18:21:46 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	John Stultz <john.stultz@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>
CC:	Ruchi Kandoi <kandoiruchi@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oren Laadan <orenl@...lrox.com>,
	Micha Kalfon <micha@...lrox.com>,
	Rom Lemarchand <romlem@...roid.com>,
	Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [RFC][PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer
 slack of an arbitrary thread.

On 6/25/2015 4:24 PM, John Stultz wrote:
> From: Ruchi Kandoi <kandoiruchi@...gle.com>
>
> This patch has been in the Android tree for ahwile, and I've not
> seen it posted for review. Unfortunately the PR_SET_TIMERSLACK_PID
> value has collided many times w/ upstream (first w/
> PR_SET_THP_DISABLE, and again w/ PR_MPX_ENABLE_MANAGEMENT).
>
> So to try to avoid further ABI trouble, I wanted to send this out
> for initial review to see if there were any major objections,
> or ideas for alternative approaches.
>
> Thoughts and feedback would be appreciated.

I am wondering if it would be more natural to make this a cgroup
property.. and have a way for threads to inherit their cgroup
effective value.

it'll fit more natural in many places than just a per pid setting.
(I have nothing against it per se other than that I think the
security check is wrong; I fully expected to be on the level of
ptrace_may_access(PTRACE_MODE_ATTACH) or the like.. not just NICE.
you can seriously change task behavior with this by setting a 4 second
value or so.. much more than just with nice)




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