iwl3945 : fix rate scaling

Patch fixes the bug 1900 at
http://www.intellinuxwireless.org/bugzilla/show_bug.cgi?id=1900

Issues:
Throughput and success ratio calculations were not done properly.
Number of retries were exceeding 16.

Fix:
Patch fixes above issues by doing window calculations inline with iwlwifi
Patch adds sanity check to limit number of retries to 16.

Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Acked-by: Mohamed Abbas <mohamed.abbas@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --git a/drivers/net/wireless/iwlwifi/iwl-3945-rs.c b/drivers/net/wireless/iwlwifi/iwl-3945-rs.c
index a266458..f65c308 100644 (file)
--- a/drivers/net/wireless/iwlwifi/iwl-3945-rs.c
+++ b/drivers/net/wireless/iwlwifi/iwl-3945-rs.c
@@ -127,6 +127,7 @@ static struct iwl3945_tpt_entry iwl3945_tpt_table_g[] = {
 #define IWL_RATE_MIN_FAILURE_TH       8
 #define IWL_RATE_MIN_SUCCESS_TH       8
 #define IWL_RATE_DECREASE_TH       1920
+#define IWL_RATE_RETRY_TH           15
 
 static u8 iwl3945_get_rate_index_by_rssi(s32 rssi, enum ieee80211_band band)
 {
@@ -298,37 +299,53 @@ static void iwl3945_collect_tx_data(struct iwl3945_rs_sta *rs_sta,
        }
 
        spin_lock_irqsave(&rs_sta->lock, flags);
-       while (retries--) {
 
-               /* If we have filled up the window then subtract one from the
-                * success counter if the high-bit is counting toward
-                * success */
-               if (window->counter == IWL_RATE_MAX_WINDOW) {
-                       if (window->data & (1ULL << (IWL_RATE_MAX_WINDOW - 1)))
+       /*
+        * Keep track of only the latest 62 tx frame attempts in this rate's
+        * history window; anything older isn't really relevant any more.
+        * If we have filled up the sliding window, drop the oldest attempt;
+        * if the oldest attempt (highest bit in bitmap) shows "success",
+        * subtract "1" from the success counter (this is the main reason
+        * we keep these bitmaps!).
+        * */
+       while (retries > 0) {
+               if (window->counter >= IWL_RATE_MAX_WINDOW) {
+
+                       /* remove earliest */
+                       window->counter = IWL_RATE_MAX_WINDOW - 1;
+
+                       if (window->data & (1ULL << (IWL_RATE_MAX_WINDOW - 1))) {
+                               window->data &= ~(1ULL << (IWL_RATE_MAX_WINDOW - 1));
                                window->success_counter--;
-               } else
-                       window->counter++;
+                       }
+               }
 
-               /* Slide the window to the left one bit */
-               window->data = (window->data << 1);
+               /* Increment frames-attempted counter */
+               window->counter++;
 
-               /* If this packet was a success then set the low bit high */
-               if (success) {
+               /* Shift bitmap by one frame (throw away oldest history),
+                * OR in "1", and increment "success" if this
+                * frame was successful. */
+               window->data <<= 1;
+               if (success > 0) {
                        window->success_counter++;
-                       window->data |= 1;
+                       window->data |= 0x1;
+                       success--;
                }
 
-               /* window->counter can't be 0 -- it is either >0 or
-                * IWL_RATE_MAX_WINDOW */
-               window->success_ratio = 12800 * window->success_counter /
-                   window->counter;
-
-               /* Tag this window as having been updated */
-               window->stamp = jiffies;
-
+               retries--;
        }
 
+       /* Calculate current success ratio, avoid divide-by-0! */
+       if (window->counter > 0)
+               window->success_ratio = 128 * (100 * window->success_counter)
+                                       / window->counter;
+       else
+               window->success_ratio = IWL_INVALID_VALUE;
+
        fail_count = window->counter - window->success_counter;
+
+       /* Calculate average throughput, if we have enough history. */
        if ((fail_count >= IWL_RATE_MIN_FAILURE_TH) ||
            (window->success_counter >= IWL_RATE_MIN_SUCCESS_TH))
                window->average_tpt = ((window->success_ratio *
@@ -336,6 +353,9 @@ static void iwl3945_collect_tx_data(struct iwl3945_rs_sta *rs_sta,
        else
                window->average_tpt = IWL_INVALID_VALUE;
 
+       /* Tag this window as having been updated */
+       window->stamp = jiffies;
+
        spin_unlock_irqrestore(&rs_sta->lock, flags);
 
 }
@@ -468,7 +488,10 @@ static void rs_tx_status(void *priv_rate, struct ieee80211_supported_band *sband
 
        IWL_DEBUG_RATE(priv, "enter\n");
 
-       retries = info->status.rates[0].count;
+       retries = info->status.rates[0].count - 1;
+       /* Sanity Check for retries */
+       if (retries > IWL_RATE_RETRY_TH)
+               retries = IWL_RATE_RETRY_TH;
 
        first_index = sband->bitrates[info->status.rates[0].idx].hw_value;
        if ((first_index < 0) || (first_index >= IWL_RATE_COUNT_3945)) {
@@ -724,7 +747,7 @@ static void rs_get_rate(void *priv_r, struct ieee80211_sta *sta,
 
        fail_count = window->counter - window->success_counter;
 
-       if (((fail_count <= IWL_RATE_MIN_FAILURE_TH) &&
+       if (((fail_count < IWL_RATE_MIN_FAILURE_TH) &&
             (window->success_counter < IWL_RATE_MIN_SUCCESS_TH))) {
                spin_unlock_irqrestore(&rs_sta->lock, flags);
 
@@ -735,6 +758,9 @@ static void rs_get_rate(void *priv_r, struct ieee80211_sta *sta,
                               window->counter,
                               window->success_counter,
                               rs_sta->expected_tpt ? "not " : "");
+
+          /* Can't calculate this yet; not enough history */
+               window->average_tpt = IWL_INVALID_VALUE;
                goto out;
 
        }
@@ -750,6 +776,7 @@ static void rs_get_rate(void *priv_r, struct ieee80211_sta *sta,
        if ((max_rate_idx != -1) && (max_rate_idx < high))
                high = IWL_RATE_INVALID;
 
+       /* Collect Measured throughputs of adjacent rates */
        if (low != IWL_RATE_INVALID)
                low_tpt = rs_sta->win[low].average_tpt;
 
@@ -758,24 +785,43 @@ static void rs_get_rate(void *priv_r, struct ieee80211_sta *sta,
 
        spin_unlock_irqrestore(&rs_sta->lock, flags);
 
-       scale_action = 1;
+       scale_action = 0;
 
+       /* Low success ratio , need to drop the rate */
        if ((window->success_ratio < IWL_RATE_DECREASE_TH) || !current_tpt) {
                IWL_DEBUG_RATE(priv, "decrease rate because of low success_ratio\n");
                scale_action = -1;
+
+       /* No throughput measured yet for adjacent rates,
+        * try increase */
        } else if ((low_tpt == IWL_INVALID_VALUE) &&
-                  (high_tpt == IWL_INVALID_VALUE))
-               scale_action = 1;
-       else if ((low_tpt != IWL_INVALID_VALUE) &&
+                  (high_tpt == IWL_INVALID_VALUE)) {
+
+               if (high != IWL_RATE_INVALID && window->success_counter >= IWL_RATE_INCREASE_TH)
+                       scale_action = 1;
+               else if (low != IWL_RATE_INVALID)
+                       scale_action = -1;
+
+       /* Both adjacent throughputs are measured, but neither one has
+        * better throughput; we're using the best rate, don't change
+        * it! */
+       } else if ((low_tpt != IWL_INVALID_VALUE) &&
                 (high_tpt != IWL_INVALID_VALUE) &&
                 (low_tpt < current_tpt) && (high_tpt < current_tpt)) {
+
                IWL_DEBUG_RATE(priv, "No action -- low [%d] & high [%d] < "
                               "current_tpt [%d]\n",
                               low_tpt, high_tpt, current_tpt);
                scale_action = 0;
+
+       /* At least one of the rates has better throughput */
        } else {
                if (high_tpt != IWL_INVALID_VALUE) {
-                       if (high_tpt > current_tpt)
+
+                       /* High rate has better throughput, Increase
+                        * rate */
+                       if (high_tpt > current_tpt &&
+                               window->success_ratio >= IWL_RATE_INCREASE_TH)
                                scale_action = 1;
                        else {
                                IWL_DEBUG_RATE(priv,
@@ -787,29 +833,31 @@ static void rs_get_rate(void *priv_r, struct ieee80211_sta *sta,
                                IWL_DEBUG_RATE(priv,
                                    "decrease rate because of low tpt\n");
                                scale_action = -1;
-                       } else
+                       } else if (window->success_counter >= IWL_RATE_INCREASE_TH) {
+                               /* Lower rate has better
+                                * throughput,decrease rate */
                                scale_action = 1;
+                       }
                }
        }
 
-       if (scale_action == -1) {
-               if (window->success_ratio > IWL_SUCCESS_DOWN_TH)
-                       scale_action = 0;
-       } else if (scale_action == 1) {
-               if (window->success_ratio < IWL_SUCCESS_UP_TH) {
-                       IWL_DEBUG_RATE(priv, "No action -- success_ratio [%d] < "
-                              "SUCCESS UP\n", window->success_ratio);
-                       scale_action = 0;
-               }
-       }
+       /* Sanity check; asked for decrease, but success rate or throughput
+        * has been good at old rate.  Don't change it. */
+       if ((scale_action == -1) && (low != IWL_RATE_INVALID) &&
+                   ((window->success_ratio > IWL_RATE_HIGH_TH) ||
+                    (current_tpt > (100 * rs_sta->expected_tpt[low]))))
+               scale_action = 0;
 
        switch (scale_action) {
        case -1:
+
+               /* Decrese rate */
                if (low != IWL_RATE_INVALID)
                        index = low;
                break;
 
        case 1:
+               /* Increase rate */
                if (high != IWL_RATE_INVALID)
                        index = high;
 
@@ -817,6 +865,7 @@ static void rs_get_rate(void *priv_r, struct ieee80211_sta *sta,
 
        case 0:
        default:
+               /* No change */
                break;
        }