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

From	Arjan van de Ven <arjan@linux.intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack of an arbitrary thread.
Date	2016-02-06 03:20 +0100
Message-ID	<qZ0DD-Aw-9@gated-at.bofh.it> (permalink)
References	(4 earlier) <qYVkB-572-11@gated-at.bofh.it> <qYVuh-5aD-3@gated-at.bofh.it> <qYVDY-5dV-5@gated-at.bofh.it> <qYXcJ-6kF-3@gated-at.bofh.it> <qYZoe-7TF-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 2/5/2016 4:51 PM, John Stultz wrote:
> On Fri, Feb 5, 2016 at 2:35 PM, John Stultz <john.stultz@linaro.org> wrote:
>> On Fri, Feb 5, 2016 at 12:50 PM, Andrew Morton
>> <akpm@linux-foundation.org> wrote:
>>> On Fri, 5 Feb 2016 12:44:04 -0800 Kees Cook <keescook@chromium.org> wrote:
>>>> Could this be exposed as a writable /proc entry instead? Like the oom_* stuff?
>>>
>>> /proc/<pid>/timer_slack_ns, guarded by ptrace_may_access(), documented
>>> under Documentation/?  Yup, that would work.  It's there for all
>>> architectures from day one and there is precedent.  It's not as nice,
>>> but /proc nasties will always be with us.
>>
>> Ok. I'll start working on that.
>
> Arjan/Thomas:  One curious thing I noticed here while writing some
> documentation. The timer_slack_ns value in the task struct is a
> unsigned long.
>
> So this means PR_SET_TIMERSLACK limits the maximum slack on 32 bit
> machines to ~4 seconds. Where on 64bit machines it can be quite a bit
> longer (unreasonably long, really :).

originally when we created timerslack, 4 seconds was an eternity and good enough for everyone
by a mile... (assumption was practical upper limit being in the 15 msec range)
and most of the RT guys would only tolerate a little bit of it

is there any real/practial use of going longer than 4 seconds? if there
is then yeah fixing it makes sense.
if it's just theoretical... shrug... 32 bit systems have a bunch of
other limits/differences a well.

Thread

[PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack of an arbitrary thread. John Stultz <john.stultz@linaro.org> - 2016-02-05 19:10 +0100
  Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack  of an arbitrary thread. Kees Cook <keescook@chromium.org> - 2016-02-05 21:20 +0100
    Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack  of an arbitrary thread. John Stultz <john.stultz@linaro.org> - 2016-02-05 21:20 +0100
  Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer  slack of an arbitrary thread. Andrew Morton <akpm@linux-foundation.org> - 2016-02-05 21:20 +0100
    Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack  of an arbitrary thread. John Stultz <john.stultz@linaro.org> - 2016-02-05 21:30 +0100
      Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer  slack of an arbitrary thread. Andrew Morton <akpm@linux-foundation.org> - 2016-02-05 21:40 +0100
        Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack  of an arbitrary thread. John Stultz <john.stultz@linaro.org> - 2016-02-05 21:40 +0100
          Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack  of an arbitrary thread. Kees Cook <keescook@chromium.org> - 2016-02-05 21:50 +0100
            Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer  slack of an arbitrary thread. Andrew Morton <akpm@linux-foundation.org> - 2016-02-05 22:00 +0100
              Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack  of an arbitrary thread. John Stultz <john.stultz@linaro.org> - 2016-02-05 23:40 +0100
                Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack  of an arbitrary thread. John Stultz <john.stultz@linaro.org> - 2016-02-06 02:00 +0100
                Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer  slack of an arbitrary thread. Andrew Morton <akpm@linux-foundation.org> - 2016-02-06 03:00 +0100
                Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack  of an arbitrary thread. John Stultz <john.stultz@linaro.org> - 2016-02-06 03:50 +0100
                Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack  of an arbitrary thread. Arjan van de Ven <arjan@linux.intel.com> - 2016-02-06 03:20 +0100
                Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack  of an arbitrary thread. Arjan van de Ven <arjan@linux.intel.com> - 2016-02-06 04:00 +0100
                Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack  of an arbitrary thread. John Stultz <john.stultz@linaro.org> - 2016-02-06 04:00 +0100

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