Commit ad018375 authored by Mattias Nissler's avatar Mattias Nissler Committed by David S. Miller
Browse files

mac80211: add PID controller based rate control algorithm



Add a new rate control algorithm based on a PID controller. It samples the
percentage of failed frames over time, feeds the result into the controller and
uses its output to control the TX rate.
Signed-off-by: default avatarMattias Nissler <mattias.nissler@gmx.de>
Signed-off-by: default avatarJohn W. Linville <linville@tuxdriver.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1abbe498
......@@ -25,6 +25,18 @@ config MAC80211_RCSIMPLE
Say Y unless you know you will have another algorithm
available.
config MAC80211_RCPID
bool "'PID' rate control algorithm" if EMBEDDED
default y
depends on MAC80211
help
This option enables a TX rate control algorithm for
mac80211 that uses a PID controller to select the TX
rate.
Say Y unless you're sure you want to use a different
rate control algorithm.
config MAC80211_LEDS
bool "Enable LED triggers"
depends on MAC80211 && LEDS_TRIGGERS
......
......@@ -4,6 +4,7 @@ mac80211-objs-$(CONFIG_MAC80211_LEDS) += ieee80211_led.o
mac80211-objs-$(CONFIG_MAC80211_DEBUGFS) += debugfs.o debugfs_sta.o debugfs_netdev.o debugfs_key.o
mac80211-objs-$(CONFIG_NET_SCHED) += wme.o
mac80211-objs-$(CONFIG_MAC80211_RCSIMPLE) += rc80211_simple.o
mac80211-objs-$(CONFIG_MAC80211_RCPID) += rc80211_pid.o
mac80211-objs := \
ieee80211.o \
......
......@@ -1315,23 +1315,37 @@ static int __init ieee80211_init(void)
#ifdef CONFIG_MAC80211_RCSIMPLE
ret = ieee80211_rate_control_register(&mac80211_rcsimple);
if (ret)
return ret;
goto fail;
#endif
#ifdef CONFIG_MAC80211_RCPID
ret = ieee80211_rate_control_register(&mac80211_rcpid);
if (ret)
goto fail;
#endif
ret = ieee80211_wme_register();
if (ret) {
#ifdef CONFIG_MAC80211_RCSIMPLE
ieee80211_rate_control_unregister(&mac80211_rcsimple);
#endif
printk(KERN_DEBUG "ieee80211_init: failed to "
"initialize WME (err=%d)\n", ret);
return ret;
goto fail;
}
ieee80211_debugfs_netdev_init();
ieee80211_regdomain_init();
return 0;
fail:
#ifdef CONFIG_MAC80211_RCSIMPLE
ieee80211_rate_control_unregister(&mac80211_rcsimple);
#endif
#ifdef CONFIG_MAC80211_RCPID
ieee80211_rate_control_unregister(&mac80211_rcpid);
#endif
return ret;
}
static void __exit ieee80211_exit(void)
......@@ -1339,6 +1353,9 @@ static void __exit ieee80211_exit(void)
#ifdef CONFIG_MAC80211_RCSIMPLE
ieee80211_rate_control_unregister(&mac80211_rcsimple);
#endif
#ifdef CONFIG_MAC80211_RCPID
ieee80211_rate_control_unregister(&mac80211_rcpid);
#endif
ieee80211_wme_unregister();
ieee80211_debugfs_netdev_exit();
......
......@@ -61,6 +61,9 @@ struct rate_control_ref {
/* default 'simple' algorithm */
extern struct rate_control_ops mac80211_rcsimple;
/* 'PID' algorithm */
extern struct rate_control_ops mac80211_rcpid;
int ieee80211_rate_control_register(struct rate_control_ops *ops);
void ieee80211_rate_control_unregister(struct rate_control_ops *ops);
......
/*
* Copyright 2002-2005, Instant802 Networks, Inc.
* Copyright 2005, Devicescape Software, Inc.
* Copyright 2007, Mattias Nissler <mattias.nissler@gmx.de>
*
* 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 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).
*
* 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)
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_info {
/* The failed frames percentage target. */
u32 target;
/* P, I and D coefficients. */
s32 coeff_p;
s32 coeff_i;
s32 coeff_d;
};
static void rate_control_pid_adjust_rate(struct ieee80211_local *local,
struct sta_info *sta, int adj)
{
struct ieee80211_sub_if_data *sdata;
struct ieee80211_hw_mode *mode;
int newidx = sta->txrate + adj;
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;
if (newidx < 0)
newidx = 0;
else if (newidx >= mode->num_rates)
newidx = mode->num_rates - 1;
while (newidx != sta->txrate) {
if (rate_supported(sta, mode, newidx) &&
(maxrate < 0 || newidx <= maxrate)) {
sta->txrate = newidx;
break;
}
newidx += back;
}
}
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;
u32 pf;
s32 err_avg;
s32 err_prop;
s32 err_int;
s32 err_der;
int adj;
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;
}
/* 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);
/* 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);
/* Change rate. */
if (adj)
rate_control_pid_adjust_rate(local, sta, adj);
}
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;
pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
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;
return pinfo;
}
static void rate_control_pid_free(void *priv)
{
struct rc_pid_info *pinfo = priv;
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,
};
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