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Date: Wed, 27 Jan 2016 12:14:14 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: John Stultz <john.stultz@linaro.org>
cc: lkml <linux-kernel@vger.kernel.org>, Ruchi Kandoi <kandoiruchi@google.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Oren Laadan <orenl@cellrox.com>, Micha Kalfon <micha@cellrox.com>,
        Rom Lemarchand <romlem@android.com>,
        Android Kernel Team <kernel-team@android.com>
Subject: Re: [RFC][PATCH v2] prctl: Add PR_SET_TIMERSLACK_PID for setting
 timer slack of an arbitrary thread.
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On Mon, 25 Jan 2016, John Stultz wrote:
> From: Ruchi Kandoi <kandoiruchi@google.com>
> 
> This allows power/performance management software to set timer
> slack for other threads according to its policy for the thread
> (such as when the thread is designated foreground vs. background
> activity)
> 
> Second argument is similar to PR_SET_TIMERSLACK, if non-zero
> then the slack is set to that value otherwise sets it to the
> default for the thread.
> 
> Takes PID of the thread as the third argument.
> 
> This interface checks that the calling task has permissions to
> to use PTRACE_MODE_ATTACH on the target task, so that we can
> ensure arbitrary apps do not change the timer slack for other
> apps.
> 
> Additional fixes from Ruchi and Micha Kalfon <micha@cellrox.com>
> have been folded into this patch to make it easier to reivew.
> 
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Oren Laadan <orenl@cellrox.com>
> Cc: Micha Kalfon <micha@cellrox.com>
> Cc: Ruchi Kandoi <kandoiruchi@google.com>
> Cc: Rom Lemarchand <romlem@android.com>
> Cc: Android Kernel Team <kernel-team@android.com>
> Signed-off-by: Ruchi Kandoi <kandoiruchi@google.com>
> [jstultz:
>  * Folded in CAP_SYS_NICE check from Ruchi.
>  * Folded in fix misplaced PR_SET_TIMERSLACK_PID case fix from
>    Micha.
>  * Folded in make PR_SET_TIMERSLACK_PID pid namespace aware fix
>    from Micha.
>  * Changed PR_SET_TIMERSLACK_PID so it didn't collide with
>    already upstream prctrl values.
>  * Reworked commit message.
>  * Moved from CAP_SYS_NICE to PTRACE_MODE_ATTACH for permissions
>    checks]
> Signed-off-by: John Stultz <john.stultz@linaro.org>

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>