/*
* Copyright 2002-2005, Instant802 Networks, Inc.
* Copyright 2005, Devicescape Software, Inc.
* Copyright 2007, Mattias Nissler <mattias.nissler@gmx.de>
* Copyright 2007, Stefano Brivio <stefano.brivio@polimi.it>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/netdevice.h>
#include <linux/types.h>
#include <linux/skbuff.h>
#include <net/mac80211.h>
#include "ieee80211_rate.h"
/* This is an implementation of a TX rate control algorithm that uses a PID
* controller. Given a target failed frames rate, the controller decides about
* TX rate changes to meet the target failed frames rate.
*
* The controller basically computes the following:
*
* adj = CP * err + CI * err_avg + CD * (err - last_err)
*
* 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
* CP Proportional coefficient
* CI Integral coefficient
* CD Derivative coefficient
*
* CP, CI, CD are subject to careful tuning.
*
* The integral component uses a exponential moving average approach instead of
* an actual sliding window. The advantage is that we don't need to keep an
* array of the last N error values and computation is easier.
*
* Once we have the adj value, we map it to a rate by means of a learning
* algorithm. This algorithm keeps the state of the percentual failed frames
* difference between rates. The behaviour of the lowest available rate is kept
* as a reference value, and every time we switch between two rates, we compute
* the difference between the failed frames each rate exhibited. By doing so,
* we compare behaviours which different rates exhibited in adjacent timeslices,
* thus the comparison is minimally affected by external conditions. This
* difference gets propagated to the whole set of measurements, so that the
* reference is always the same. Periodically, we normalize this set so that
* recent events weigh the most. By comparing the adj value with this set, we
* avoid pejorative switches to lower rates and allow for switches to higher
* rates if they behaved well.
*
* Note that for the computations we use a fixed-point representation to avoid
* floating point arithmetic. Hence, all values are shifted left by
* RC_PID_ARITH_SHIFT.
*/
/* Sampling period for measuring percentage of failed frames. */
#define RC_PID_INTERVAL (HZ / 8)
/* Exponential averaging smoothness (used for I part of PID controller) */
#define RC_PID_SMOOTHING_SHIFT 3
#define RC_PID_SMOOTHING (1 << RC_PID_SMOOTHING_SHIFT)
/* Fixed point arithmetic shifting amount. */
#define RC_PID_ARITH_SHIFT 8
/* Fixed point arithmetic factor. */
#define RC_PID_ARITH_FACTOR (1 << RC_PID_ARITH_SHIFT)
/* Proportional PID component coefficient. */
#define RC_PID_COEFF_P 15
/* Integral PID component coefficient. */
#define RC_PID_COEFF_I 9
/* Derivative PID component coefficient. */
#define RC_PID_COEFF_D 15
/* Target failed frames rate for the PID controller. NB: This effectively gives
* maximum failed frames percentage we're willing to accept. If the wireless
* link quality is good, the controller will fail to adjust failed frames
* percentage to the target. This is intentional.
*/
#define RC_PID_TARGET_PF (11 << RC_PID_ARITH_SHIFT)
/* Rate behaviour normalization quantity over time. */
#define RC_PID_NORM_OFFSET 3
/* Push high rates right after loading. */
#define RC_PID_FAST_START 0
/* Arithmetic right shift for positive and negative values for ISO C. */
#define RC_PID_DO_ARITH_RIGHT_SHIFT(x, y) \
(x) < 0 ? -((-(x)) >> (y)) : (x) >> (y)
struct rc_pid_sta_info {
unsigned long last_change;
unsigned long last_sample;
u32 tx_num_failed;
u32 tx_num_xmit;
/* Average failed frames percentage error (i.e. actual vs. target
* percentage), scaled by RC_PID_SMOOTHING. This value is computed
* using using an exponential weighted average technique:
*
* (RC_PID_SMOOTHING - 1) * err_avg_old + err
* err_avg = ------------------------------------------
* RC_PID_SMOOTHING
*
* where err_avg is the new approximation, err_avg_old the previous one
* and err is the error w.r.t. to the current failed frames percentage
* sample. Note that the bigger RC_PID_SMOOTHING the more weight is
* given to the previous estimate, resulting in smoother behavior (i.e.
* corresponding to a longer integration window).
*
* For computation, we actually don't use the above formula, but this
* one:
*
* err_avg_scaled = err_avg_old_scaled - err_avg_old + err
*
* where:
* err_avg_scaled = err * RC_PID_SMOOTHING
* err_avg_old_scaled = err_avg_old * RC_PID_SMOOTHING
*
* This avoids floating point numbers and the per_failed_old value can
* easily be obtained by shifting per_failed_old_scaled right by
* RC_PID_SMOOTHING_SHIFT.
*/
s32 err_avg_sc;
/* Last framed failes percentage sample */
u32 last_pf;
};
/* Algorithm parameters. We keep them on a per-algorithm approach, so they can
* be tuned individually for each interface.
*/
struct rc_pid_rateinfo {
/* Map sorted rates to rates in ieee80211_hw_mode. */
int index;
/* Map rates in ieee80211_hw_mode to sorted rates. */
int rev_index;
/* Comparison with the lowest rate. */
int diff;
};
struct rc_pid_info {
/* The failed frames percentage target. */
u32 target;
/* P, I and D coefficients. */
s32 coeff_p;
s32 coeff_i;
s32 coeff_d;
/* Rates information. */
struct rc_pid_rateinfo *rinfo;
/* Index of the last used rate. */
int oldrate;
};
/* Shift the adjustment so that we won't switch to a lower rate if it exhibited
* a worse failed frames behaviour and we'll choose the highest rate whose
* failed frames behaviour is not worse than the one of the original rate
* target. While at it, check that the adjustment is within the ranges. Then,
* provide the new rate index. */
static int rate_control_pid_shift_adjust(struct rc_pid_rateinfo *r,
int adj, int cur, int l)
{
int i, j, k, tmp;
if (cur + adj < 0)
return 0;
if (cur + adj >= l)
return l - 1;
i = r[cur + adj].rev_index;
j = r[cur].rev_index;
if (adj < 0) {
tmp = i;
for (k = j; k >= i; k--)
if (r[k].diff <= r[j].diff)
tmp = k;
return r[tmp].index;
} else if (adj > 0) {
tmp = i;
for (k = i + 1; k + i < l; k++)
if (r[k].diff <= r[i].diff)
tmp = k;
return r[tmp].index;
}
return cur + adj;
}
static void rate_control_pid_adjust_rate(struct ieee80211_local *local,
struct sta_info *sta, int adj,
struct rc_pid_rateinfo *rinfo)
{
struct ieee80211_sub_if_data *sdata;
struct ieee80211_hw_mode *mode;
int newidx;
int maxrate;
int back = (adj > 0) ? 1 : -1;
sdata = IEEE80211_DEV_TO_SUB_IF(sta->dev);
if (sdata->bss && sdata->bss->force_unicast_rateidx > -1) {
/* forced unicast rate - do not change STA rate */
return;
}
mode = local->oper_hw_mode;
maxrate = sdata->bss ? sdata->bss->max_ratectrl_rateidx : -1;
newidx = rate_control_pid_shift_adjust(rinfo, adj, sta->txrate,
mode->num_rates);
while (newidx != sta->txrate) {
if (rate_supported(sta, mode, newidx) &&
(maxrate < 0 || newidx <= maxrate)) {
sta->txrate = newidx;
break;
}
newidx += back;
}
}
/* Normalize the failed frames per-rate differences. */
static void rate_control_pid_normalize(struct rc_pid_rateinfo *r, int l)
{
int i;
if (r[0].diff > RC_PID_NORM_OFFSET)
r[0].diff -= RC_PID_NORM_OFFSET;
else if (r[0].diff < -RC_PID_NORM_OFFSET)
r[0].diff += RC_PID_NORM_OFFSET;
for (i = 0; i < l - 1; i++)
if (r[i + 1].diff > r[i].diff + RC_PID_NORM_OFFSET)
r[i + 1].diff -= RC_PID_NORM_OFFSET;
else if (r[i + 1].diff <= r[i].diff)
r[i + 1].diff += RC_PID_NORM_OFFSET;
}
static void rate_control_pid_sample(struct rc_pid_info *pinfo,
struct ieee80211_local *local,
struct sta_info *sta)
{
struct rc_pid_sta_info *spinfo = sta->rate_ctrl_priv;
struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
struct ieee80211_hw_mode *mode;
u32 pf;
s32 err_avg;
s32 err_prop;
s32 err_int;
s32 err_der;
int adj, i, j, tmp;
mode = local->oper_hw_mode;
spinfo = sta->rate_ctrl_priv;
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;
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;
}
/* If we just switched rate, update the rate behaviour info. */
if (pinfo->oldrate != sta->txrate) {
i = rinfo[pinfo->oldrate].rev_index;
j = rinfo[sta->txrate].rev_index;
tmp = (pf - spinfo->last_pf);
tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);
rinfo[j].diff = rinfo[i].diff + tmp;
pinfo->oldrate = sta->txrate;
}
rate_control_pid_normalize(rinfo, mode->num_rates);
/* Compute the proportional, integral and derivative errors. */
err_prop = RC_PID_TARGET_PF - pf;
err_avg = spinfo->err_avg_sc >> RC_PID_SMOOTHING_SHIFT;
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;
spinfo->last_pf = pf;
/* Compute the controller output. */
adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
+ err_der * pinfo->coeff_d);
adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);
/* Change rate. */
if (adj)
rate_control_pid_adjust_rate(local, sta, adj, rinfo);
}
static void rate_control_pid_tx_status(void *priv, struct net_device *dev,
struct sk_buff *skb,
struct ieee80211_tx_status *status)
{
struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
struct rc_pid_info *pinfo = priv;
struct sta_info *sta;
struct rc_pid_sta_info *spinfo;
sta = sta_info_get(local, hdr->addr1);
if (!sta)
return;
/* Ignore all frames that were sent with a different rate than the rate
* we currently advise mac80211 to use. */
if (status->control.rate != &local->oper_hw_mode->rates[sta->txrate])
return;
spinfo = sta->rate_ctrl_priv;
spinfo->tx_num_xmit++;
/* We count frames that totally failed to be transmitted as two bad
* frames, those that made it out but had some retries as one good and
* one bad frame. */
if (status->excessive_retries) {
spinfo->tx_num_failed += 2;
spinfo->tx_num_xmit++;
} else if (status->retry_count) {
spinfo->tx_num_failed++;
spinfo->tx_num_xmit++;
}
if (status->excessive_retries) {
sta->tx_retry_failed++;
sta->tx_num_consecutive_failures++;
sta->tx_num_mpdu_fail++;
} else {
sta->last_ack_rssi[0] = sta->last_ack_rssi[1];
sta->last_ack_rssi[1] = sta->last_ack_rssi[2];
sta->last_ack_rssi[2] = status->ack_signal;
sta->tx_num_consecutive_failures = 0;
sta->tx_num_mpdu_ok++;
}
sta->tx_retry_count += status->retry_count;
sta->tx_num_mpdu_fail += status->retry_count;
/* Update PID controller state. */
if (time_after(jiffies, spinfo->last_sample + RC_PID_INTERVAL))
rate_control_pid_sample(pinfo, local, sta);
sta_info_put(sta);
}
static void rate_control_pid_get_rate(void *priv, struct net_device *dev,
struct ieee80211_hw_mode *mode,
struct sk_buff *skb,
struct rate_selection *sel)
{
struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
struct sta_info *sta;
int rateidx;
sta = sta_info_get(local, hdr->addr1);
if (!sta) {
sel->rate = rate_lowest(local, mode, NULL);
sta_info_put(sta);
return;
}
rateidx = sta->txrate;
if (rateidx >= mode->num_rates)
rateidx = mode->num_rates - 1;
sta_info_put(sta);
sel->rate = &mode->rates[rateidx];
}
static void rate_control_pid_rate_init(void *priv, void *priv_sta,
struct ieee80211_local *local,
struct sta_info *sta)
{
/* TODO: This routine should consider using RSSI from previous packets
* as we need to have IEEE 802.1X auth succeed immediately after assoc..
* Until that method is implemented, we will use the lowest supported
* rate as a workaround. */
sta->txrate = rate_lowest_index(local, local->oper_hw_mode, sta);
}
static void *rate_control_pid_alloc(struct ieee80211_local *local)
{
struct rc_pid_info *pinfo;
struct rc_pid_rateinfo *rinfo;
struct ieee80211_hw_mode *mode;
int i, j, tmp;
bool s;
pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
if (!pinfo)
return NULL;
/* We can safely assume that oper_hw_mode won't change unless we get
* reinitialized. */
mode = local->oper_hw_mode;
rinfo = kmalloc(sizeof(*rinfo) * mode->num_rates, GFP_ATOMIC);
if (!rinfo) {
kfree(pinfo);
return NULL;
}
/* Sort the rates. This is optimized for the most common case (i.e.
* almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
* mapping too. */
for (i = 0; i < mode->num_rates; i++) {
rinfo[i].index = i;
rinfo[i].rev_index = i;
if (RC_PID_FAST_START)
rinfo[i].diff = 0;
else
rinfo[i].diff = i * RC_PID_NORM_OFFSET;
}
for (i = 1; i < mode->num_rates; i++) {
s = 0;
for (j = 0; j < mode->num_rates - i; j++)
if (unlikely(mode->rates[rinfo[j].index].rate >
mode->rates[rinfo[j + 1].index].rate)) {
tmp = rinfo[j].index;
rinfo[j].index = rinfo[j + 1].index;
rinfo[j + 1].index = tmp;
rinfo[rinfo[j].index].rev_index = j;
rinfo[rinfo[j + 1].index].rev_index = j + 1;
s = 1;
}
if (!s)
break;
}
pinfo->target = RC_PID_TARGET_PF;
pinfo->coeff_p = RC_PID_COEFF_P;
pinfo->coeff_i = RC_PID_COEFF_I;
pinfo->coeff_d = RC_PID_COEFF_D;
pinfo->rinfo = rinfo;
pinfo->oldrate = 0;
return pinfo;
}
static void rate_control_pid_free(void *priv)
{
struct rc_pid_info *pinfo = priv;
kfree(pinfo->rinfo);
kfree(pinfo);
}
static void rate_control_pid_clear(void *priv)
{
}
static void *rate_control_pid_alloc_sta(void *priv, gfp_t gfp)
{
struct rc_pid_sta_info *spinfo;
spinfo = kzalloc(sizeof(*spinfo), gfp);
return spinfo;
}
static void rate_control_pid_free_sta(void *priv, void *priv_sta)
{
struct rc_pid_sta_info *spinfo = priv_sta;
kfree(spinfo);
}
struct rate_control_ops mac80211_rcpid = {
.name = "pid",
.tx_status = rate_control_pid_tx_status,
.get_rate = rate_control_pid_get_rate,
.rate_init = rate_control_pid_rate_init,
.clear = rate_control_pid_clear,
.alloc = rate_control_pid_alloc,
.free = rate_control_pid_free,
.alloc_sta = rate_control_pid_alloc_sta,
.free_sta = rate_control_pid_free_sta,
};
