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From: John Stultz <john.stultz@linaro.org>
Date: Thu, 14 Jul 2016 09:01:27 -0700
Message-ID: <CALAqxLWbqo3ha5oOvrdpR0VCfxugSuWknrGXTbEu+DE9Y0kFGg@mail.gmail.com>
Subject: Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface
To: Arjan van de Ven <arjan@linux.intel.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>, Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        lkml <linux-kernel@vger.kernel.org>, Oren Laadan <orenl@cellrox.com>,
        Ruchi Kandoi <kandoiruchi@google.com>,
        Rom Lemarchand <romlem@android.com>,
        Android Kernel Team <kernel-team@android.com>,
        Todd Kjos <tkjos@google.com>, Colin Cross <ccross@android.com>,
        Nick Kralevich <nnk@google.com>, Dmitry Shmidt <dimitrysh@google.com>,
        Elliott Hughes <enh@google.com>
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On Thu, Jul 14, 2016 at 6:42 AM, Arjan van de Ven <arjan@linux.intel.com> wrote:
> On 7/14/2016 5:48 AM, Serge E. Hallyn wrote:
>
>> Can someone give a detailed explanation of what you could do with
>> the new timerslack feature and compare it to what you can do with
>> sys_nice?
>>
>
> what you can do with the timerslack feature is add upto 4 seconds of extra
> time/delay on top of each select()/poll()/nanosleep()/... (basically
> anything that
> uses hrtimers on behalf of the user), and then also control within that
> 4 second window exactly when that extra delay ends
> (which may help a timing attack kind of scenario)

So the interface actually allows for 64bits of nanoseconds, so more or
less infinite delay if nothing else is happening.

thanks
-john