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SubjectRe: [PATCH 2/2] cpuidle: Add a repeating pattern detector to the menu governor
On Wed, 19 May 2010 12:51:50 -0700
Frank Rowand <frank.rowand@am.sony.com> wrote:

> Aplogies if this is a duplicate, my outgoing email seems to have not
> been working.
>
> On 05/09/10 16:04, Arjan van de Ven wrote:
>
> > +/*
> > + * Try detecting repeating patterns by keeping track of the last 8
> > + * intervals, and checking if the standard deviation of that set
> > + * of points is below a threshold. If it is... then use the
> > + * average of these 8 points as the estimated value.
> > + */
> > +static void detect_repeating_patterns(struct menu_device *data)
> > +{
> > + int i;
> > + uint64_t avg = 0;
> > + uint64_t stddev = 0; /* contains the square of the std deviation */
> > +
> > + /* first calculate average and standard deviation of the past */
> > + for (i = 0; i < INTERVALS; i++)
> > + avg += data->intervals[i];
> > +
> > + /* if the avg is beyond the known next tick, it's worthless */
> > + if (avg > data->expected_us)
> > + return;
> > +
>
> Should the following division by INTERVALS be moved up 6 lines to before
> "if (avg > data->expected_us)"?

Quite possibly.

> > + avg = avg / INTERVALS;
> > + for (i = 0; i < INTERVALS; i++)
> > + stddev += (data->intervals[i] - avg) *
> > + (data->intervals[i] - avg);
> > +
> > + stddev = stddev / INTERVALS;
> > +
> > + /*
> > + * now.. if stddev is small.. then assume we have a
> > + * repeating pattern and predict we keep doing this.
> > + */
> > +
> > + if (avg && stddev < STDDEV_THRESH)
> > + data->predicted_us = avg;
> > +}

wakey wakey, Arjan.


Also, expected_us is 32-bit and predicted_us is 64-bit. Was that rational?


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