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

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Message-ID: <CALAqxLWKSo29Rkn6-M-Qp_LVNxAcar84aM3M8Qg578KqJX6XYw@mail.gmail.com>
Date:	Fri, 5 Feb 2016 18:41:09 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Kees Cook <keescook@...omium.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Ruchi Kandoi <kandoiruchi@...gle.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oren Laadan <orenl@...lrox.com>,
	Rom Lemarchand <romlem@...roid.com>,
	Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack
 of an arbitrary thread.

On Fri, Feb 5, 2016 at 5:56 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Fri, 5 Feb 2016 16:51:02 -0800 John Stultz <john.stultz@...aro.org> wrote:
>> Alternatively, with the /proc/pid/timerslack_ns interface I'm working
>> on, we can make the backing storage a long long and support 64bits of
>> nanoseconds on all architectures. (But again, we can't really change
>> PR_SET/GET_TIMERSLACK, so 32bit systems might see strange values from
>> that with larger then uint slack values).
>>
>> Or I can just leave it as ULONG_MAX on all interfaces.
>>
>> Thoughts or preferences?
>
> /proc/<pid>/timer_slack_us?

So the issue isn't so much in the new interface (we can have it take a
long long), but really in the existing PR_GET/SET_TIMERSLACK. I'm just
trying to figure out if following the existing oddness is the best
approach, or if we should make the new interface do a more consistent
thing, but with the result that the PR_GET_TIMERSLACK interface might
return "incorrect" values (just the lower 32bits).

thanks
-john