rc80211-pid: add sharpening factor

This patch introduces a PID sharpening factor for faster response after
association and low activity events.

Signed-off-by: Stefano Brivio <stefano.brivio@polimi.it>
Signed-off-by: Mattias Nissler <mattias.nissler@gmx.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 27 insertions, 8 deletions

diff --git a/net/mac80211/rc80211_pid.c b/net/mac80211/rc80211_pid.c
index 1116dc67ddd0..7f8cf27ad2f9 100644
--- a/net/mac80211/rc80211_pid.c
+++ b/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 +68,10 @@
 #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 RC_PID_SHARPENING_FACTOR 0
+#define RC_PID_SHARPENING_DURATION 0
+
 /* Fixed point arithmetic shifting amount. */
 #define RC_PID_ARITH_SHIFT 8
 
@@ -131,8 +138,11 @@ 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
@@ -267,20 +277,26 @@ static void rate_control_pid_sample(struct rc_pid_info *pinfo,
 
         mode = local->oper_hw_mode;
         spinfo = sta->rate_ctrl_priv;
+
+        /* In case nothing happened during the previous control interval, turn
+         * the sharpening factor on. */
+        if (jiffies - spinfo->last_sample > 2 * RC_PID_INTERVAL)
+                spinfo->sharp_cnt = RC_PID_SHARPENING_DURATION;
+
         spinfo->last_sample = jiffies;
 
-        /* If no frames were transmitted, we assume the old sample is
+        /* This should never happen, but in case, we assume the old sample is
          * still a good measurement and copy it. */
-        if (spinfo->tx_num_xmit == 0)
+        if (unlikely(spinfo->tx_num_xmit == 0))
                 pf = spinfo->last_pf;
         else {
                 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) {
 
@@ -302,8 +318,11 @@ static void rate_control_pid_sample(struct rc_pid_info *pinfo,
         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 + RC_PID_SHARPENING_FACTOR * 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