linux-kernel - Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

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Message-ID: <729c3cfc-6f0a-fb1a-f8c7-0b7860a3d22e@linux.intel.com>
Date:   Thu, 20 Jul 2017 06:45:58 -0700
From:   Arjan van de Ven <arjan@...ux.intel.com>
To:     paulmck@...ux.vnet.ibm.com,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Aubrey Li <aubrey.li@...el.com>, len.brown@...el.com,
        rjw@...ysocki.net, tim.c.chen@...ux.intel.com,
        yang.zhang.wz@...il.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, daniel.lezcano@...aro.org
Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

On 7/20/2017 5:50 AM, Paul E. McKenney wrote:
> To make this work reasonably, you would also need some way to check for
> the case where the prediction idle time is short but the real idle time
> is very long.

so the case where you predict very short but is actually "indefinite", the real
solution likely is that we set a timer some time in the future
(say 100msec, or some other value that is long but not indefinite)
where we wake up the system and make a new prediction,
since clearly we were insanely wrong in the prediction and should try
again.

that or we turn the prediction from a single value into a range of
(expected, upper bound)

where upper bound is likely the next timer or other going-to-happen events.