linux-kernel - Re: [RFC/RFT][PATCH v5] cpuidle: New timer events oriented governor for tickless systems

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Date:   Thu, 15 Nov 2018 03:57:05 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Doug Smythies <dsmythies@...us.net>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Mel Gorman <mgorman@...e.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [RFC/RFT][PATCH v5] cpuidle: New timer events oriented governor for tickless systems

On Sunday, November 11, 2018 4:20:34 PM CET Peter Zijlstra wrote:
> On Thu, Nov 08, 2018 at 06:25:07PM +0100, Rafael J. Wysocki wrote:
> > +/*
> > + * The SPIKE value is added to metrics when they grow and the DECAY_SHIFT value
> > + * is used for decreasing metrics on a regular basis.
> > + */
> > +#define SPIKE		1024
> > +#define DECAY_SHIFT	3
> 
> > +	if (idx_timer >= 0) {
> > +		unsigned int hits = cpu_data->states[idx_timer].hits;
> > +		unsigned int misses = cpu_data->states[idx_timer].misses;
> > +
> > +		hits -= hits >> DECAY_SHIFT;
> > +		misses -= misses >> DECAY_SHIFT;
> > +
> > +		if (idx_timer > idx_hit) {
> > +			misses += SPIKE;
> > +			if (idx_hit >= 0)
> > +				cpu_data->states[idx_hit].early_hits += SPIKE;
> > +		} else {
> > +			hits += SPIKE;
> > +		}
> > +
> > +		cpu_data->states[idx_timer].misses = misses;
> > +		cpu_data->states[idx_timer].hits = hits;
> > +	}
> 
> That's a pulse-density-modulator, with a signal bound of:
> 
>   1024 == x/8 -> x := 8192
> 
> Anyway; I would suggest s/SPIKE/PULSE/ because of that.

OK