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iwl3945 : fix rate scaling
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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>
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Abhijeet Kolekar authored and John W. Linville committed Mar 16, 2009
1 parent 5c8df2d commit dd5b687
Showing 1 changed file with 88 additions and 39 deletions.
127 changes: 88 additions & 39 deletions drivers/net/wireless/iwlwifi/iwl-3945-rs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
{
Expand Down Expand Up @@ -298,44 +299,63 @@ 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 *
rs_sta->expected_tpt[index] + 64) / 128);
else
window->average_tpt = IWL_INVALID_VALUE;

/* Tag this window as having been updated */
window->stamp = jiffies;

spin_unlock_irqrestore(&rs_sta->lock, flags);

}
Expand Down Expand Up @@ -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)) {
Expand Down Expand Up @@ -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);

Expand All @@ -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;

}
Expand All @@ -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;

Expand All @@ -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,
Expand All @@ -787,36 +833,39 @@ 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;

break;

case 0:
default:
/* No change */
break;
}

Expand Down

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