Commit 90d501d6 authored by Stefano Brivio's avatar Stefano Brivio Committed by David S. Miller
Browse files

rc80211-pid: add rate behaviour learning algorithm



This patch introduces a learning algorithm in order for the PID controller
to learn how to map adjustment values to rates. This is better described in
code comments.
Signed-off-by: default avatarStefano Brivio <stefano.brivio@polimi.it>
Signed-off-by: default avatarJohn W. Linville <linville@tuxdriver.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c21b39ac
......@@ -2,6 +2,7 @@
* 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
......@@ -39,12 +40,18 @@
* 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 need to map it to a TX rate to be selected.
* For now, we depend on the rates to be ordered in a way such that more robust
* rates (i.e. such that exhibit a lower framed failed percentage) come first.
* E.g. for the 802.11b/g case, we first have the b rates in ascending order,
* then the g rates. The adj simply decides the index of the TX rate in the list
* to switch to (relative to the current TX rate entry).
* 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
......@@ -78,6 +85,16 @@
*/
#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;
......@@ -121,6 +138,18 @@ struct rc_pid_sta_info {
/* 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. */
......@@ -130,15 +159,56 @@ struct rc_pid_info {
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 sta_info *sta, int adj,
struct rc_pid_rateinfo *rinfo)
{
struct ieee80211_sub_if_data *sdata;
struct ieee80211_hw_mode *mode;
int newidx = sta->txrate + adj;
int newidx;
int maxrate;
int back = (adj > 0) ? 1 : -1;
......@@ -151,10 +221,8 @@ static void rate_control_pid_adjust_rate(struct ieee80211_local *local,
mode = local->oper_hw_mode;
maxrate = sdata->bss ? sdata->bss->max_ratectrl_rateidx : -1;
if (newidx < 0)
newidx = 0;
else if (newidx >= mode->num_rates)
newidx = mode->num_rates - 1;
newidx = rate_control_pid_shift_adjust(rinfo, adj, sta->txrate,
mode->num_rates);
while (newidx != sta->txrate) {
if (rate_supported(sta, mode, newidx) &&
......@@ -167,18 +235,37 @@ static void rate_control_pid_adjust_rate(struct ieee80211_local *local,
}
}
/* 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;
int adj, i, j, tmp;
mode = local->oper_hw_mode;
spinfo = sta->rate_ctrl_priv;
spinfo->last_sample = jiffies;
......@@ -194,6 +281,20 @@ static void rate_control_pid_sample(struct rc_pid_info *pinfo,
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;
......@@ -207,16 +308,11 @@ static void rate_control_pid_sample(struct rc_pid_info *pinfo,
/* Compute the controller output. */
adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
+ err_der * pinfo->coeff_d);
/* We need to do an arithmetic right shift. ISO C says this is
* implementation defined for negative left operands. Hence, be
* careful to get it right, also for negative values. */
adj = (adj < 0) ? -((-adj) >> (2 * RC_PID_ARITH_SHIFT)) :
adj >> (2 * RC_PID_ARITH_SHIFT);
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);
rate_control_pid_adjust_rate(local, sta, adj, rinfo);
}
static void rate_control_pid_tx_status(void *priv, struct net_device *dev,
......@@ -316,13 +412,57 @@ static void rate_control_pid_rate_init(void *priv, void *priv_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;
}
......@@ -330,6 +470,7 @@ static void *rate_control_pid_alloc(struct ieee80211_local *local)
static void rate_control_pid_free(void *priv)
{
struct rc_pid_info *pinfo = priv;
kfree(pinfo->rinfo);
kfree(pinfo);
}
......
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