[RFC/T][PATCH 2/3] rc80211-pid: introduce PID sharpening factor

[Stefano Brivio <stefano.brivio@polimi.it>]

This patch introduces a PID sharpening factor for faster response on
association and interpolation.


Signed-off-by: Stefano Brivio <stefano.brivio@polimi.it>

---

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 +23,15 @@
  *
  * 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 interpolation), heading to zero over time
  * 	CP	Proportional coefficient
  * 	CI	Integral coefficient
  * 	CD	Derivative coefficient
@@ -65,6 +67,11 @@
 #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
 
@@ -127,8 +134,11 @@ 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
@@ -271,10 +281,12 @@ static void rate_control_pid_sample(stru
 	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)
+	 * still a good measurement and copy it, and turn the sharpening factor
+	 * on. */
+	if (spinfo->tx_num_xmit == 0) {
 		pf = spinfo->last_pf;
-	else {
+		spinfo->sharp_cnt = RATE_CONTROL_SHARPENING_DURATION;
+	} else {
 		pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;
 		pf <<= RC_PID_ARITH_SHIFT;
 
@@ -314,8 +326,11 @@ 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


-- 
Ciao
Stefano