Messages in this thread | | | Date | Wed, 19 May 2010 12:51:50 -0700 | From | Frank Rowand <> | Subject | Re: [PATCH 2/2] cpuidle: Add a repeating pattern detector to the menu governor |
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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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