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From: Andrew Morton on 10 May 2010 17:40
On Sun, 9 May 2010 16:04:44 -0700
Arjan van de Ven <arjan(a)infradead.org> wrote:

> +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;
> +
> + 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;
> +}

You got lucky there, because INTERVALS is a power of two. If someone
changes INTERVALS to 7, this code will ask for __udivdi3 and won't link
on i364.
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From: Arjan van de Ven on 10 May 2010 21:30
On Mon, 10 May 2010 14:38:50 -0700
Andrew Morton <akpm(a)linux-foundation.org> wrote:

> > + if (avg && stddev < STDDEV_THRESH)
> > + data->predicted_us = avg;
> > +}
>
> You got lucky there, because INTERVALS is a power of two. If someone
> changes INTERVALS to 7, this code will ask for __udivdi3 and won't
> link on i364.

yeah you'd think it almost isn't an accident ;-)


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visit http://www.lesswatts.org
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From: Andrew Morton on 10 May 2010 22:50
On Mon, 10 May 2010 18:27:46 -0700 Arjan van de Ven <arjan(a)infradead.org> wrote:

> On Mon, 10 May 2010 14:38:50 -0700
> Andrew Morton <akpm(a)linux-foundation.org> wrote:
>
> > > + if (avg && stddev < STDDEV_THRESH)
> > > + data->predicted_us = avg;
> > > +}
> >
> > You got lucky there, because INTERVALS is a power of two. If someone
> > changes INTERVALS to 7, this code will ask for __udivdi3 and won't
> > link on i364.
>
> yeah you'd think it almost isn't an accident ;-)

If it was deliberate the code would read

avg >>= INTERVALS_SHIFT;

:-p
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From: Frank Rowand on 19 May 2010 16:00
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)"?

> + 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;
> +}


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From: Andrew Morton on 21 May 2010 15:50
On Wed, 19 May 2010 12:51:50 -0700
Frank Rowand <frank.rowand(a)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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