On Mon, 2007-12-10 at 03:28 +0100, Stefano Brivio wrote:
> This patch introduces a PID sharpening factor for faster response after
> association and low activity events.
>
>
> Signed-off-by: Stefano Brivio <stefano.brivio@xxxxxxxxx>
> Cc: Mattias Nissler <mattias.nissler@xxxxxx>
>
> ---
>
> Ok, this isn't a no-op anymore. :)
>
> ---
>
> Index: wireless-2.6/net/mac80211/rc80211_pid.c
> ===================================================================
> --- wireless-2.6.orig/net/mac80211/rc80211_pid.c
> +++ wireless-2.6/net/mac80211/rc80211_pid.c
> @@ -23,13 +23,16 @@
> *
> * The controller basically computes the following:
> *
> - * adj = CP * err + CI * err_avg + CD * (err - last_err)
> + * adj = CP * err + CI * err_avg + CD * (err - last_err) * (1 + sharpening)
> *
> * where
> * adj adjustment value that is used to switch TX rate (see below)
> * err current error: target vs. current failed frames percentage
> * last_err last error
> * err_avg average (i.e. poor man's integral) of recent errors
> + * sharpening non-zero when fast response is needed (i.e. right after
> + * association or no frames sent for a long time), heading
> + * to zero over time
> * CP Proportional coefficient
> * CI Integral coefficient
> * CD Derivative coefficient
> @@ -65,6 +68,11 @@
> #define RC_PID_SMOOTHING_SHIFT 3
> #define RC_PID_SMOOTHING (1 << RC_PID_SMOOTHING_SHIFT)
>
> +/* Sharpening factor (used for D part of PID controller) */
> +#define RATE_CONTROL_SHARPENING_SHIFT 2
> +#define RATE_CONTROL_SHARPENING (1 << RATE_CONTROL_SHARPENING_SHIFT)
> +#define RATE_CONTROL_SHARPENING_DURATION 1
> +
> /* Fixed point arithmetic shifting amount. */
> #define RC_PID_ARITH_SHIFT 8
>
> @@ -131,8 +139,11 @@ struct rc_pid_sta_info {
> */
> s32 err_avg_sc;
>
> - /* Last framed failes percentage sample */
> + /* Last framed failes percentage sample. */
> u32 last_pf;
> +
> + /* Sharpening needed. */
> + u8 sharp_cnt;
> };
>
> /* Algorithm parameters. We keep them on a per-algorithm approach, so they can
> @@ -282,19 +293,19 @@ static void rate_control_pid_sample(stru
>
> mode = local->oper_hw_mode;
> spinfo = sta->rate_ctrl_priv;
> +
> + /* In case nothing happened during the previous control interval, turn
> + * on the sharpening factor. */
> + if (jiffies - spinfo->last_sample > RC_PID_INTERVAL)
> + spinfo->sharp_cnt = RATE_CONTROL_SHARPENING_DURATION;
> +
> spinfo->last_sample = jiffies;
>
> - /* If no frames were transmitted, we assume the old sample is
> - * still a good measurement and copy it. */
> - if (spinfo->tx_num_xmit == 0)
> - pf = spinfo->last_pf;
Please don't remove this check. We can never know when anybody starts
calling rate_control_pid_sample() without packets transmitted. Then it's
good to have it, else we divide by zero in the next line.
> - else {
> - pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;
> - pf <<= RC_PID_ARITH_SHIFT;
> + pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;
> + pf <<= RC_PID_ARITH_SHIFT;
>
> - spinfo->tx_num_xmit = 0;
> - spinfo->tx_num_failed = 0;
> - }
> + spinfo->tx_num_xmit = 0;
> + spinfo->tx_num_failed = 0;
>
> /* If we just switched rate, update the rate behaviour info. */
> if (pinfo->oldrate != sta->txrate) {
> @@ -321,8 +332,11 @@ static void rate_control_pid_sample(stru
> spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;
> err_int = spinfo->err_avg_sc >> RC_PID_SMOOTHING_SHIFT;
>
> - err_der = pf - spinfo->last_pf;
> + err_der = pf - spinfo->last_pf
> + * (1 + RATE_CONTROL_SHARPENING * spinfo->sharp_cnt);
> spinfo->last_pf = pf;
> + if (spinfo->sharp_cnt)
> + spinfo->sharp_cnt--;
>
> /* Compute the controller output. */
> adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
>
>
-
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