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Diffstat (limited to 'contrib/syslinux-4.02/gpxe/src/net/80211/rc80211.c')
| -rw-r--r-- | contrib/syslinux-4.02/gpxe/src/net/80211/rc80211.c | 371 |
1 files changed, 371 insertions, 0 deletions
diff --git a/contrib/syslinux-4.02/gpxe/src/net/80211/rc80211.c b/contrib/syslinux-4.02/gpxe/src/net/80211/rc80211.c new file mode 100644 index 0000000..5bd1914 --- /dev/null +++ b/contrib/syslinux-4.02/gpxe/src/net/80211/rc80211.c @@ -0,0 +1,371 @@ +/* + * Simple 802.11 rate-control algorithm for gPXE. + * + * Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.net>. + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License as + * published by the Free Software Foundation; either version 2 of the + * License, or any later version. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + */ + +FILE_LICENCE ( GPL2_OR_LATER ); + +#include <stdlib.h> +#include <gpxe/net80211.h> + +/** + * @file + * + * Simple 802.11 rate-control algorithm + */ + +/** @page rc80211 Rate control philosophy + * + * We want to maximize our transmission speed, to the extent that we + * can do that without dropping undue numbers of packets. We also + * don't want to take up very much code space, so our algorithm has to + * be pretty simple + * + * When we receive a packet, we know what rate it was transmitted at, + * and whether it had to be retransmitted to get to us. + * + * When we send a packet, we hear back how many times it had to be + * retried to get through, and whether it got through at all. + * + * Indications of TX success are more reliable than RX success, but RX + * information helps us know where to start. + * + * To handle all of this, we keep for each rate and each direction (TX + * and RX separately) some state information for the most recent + * packets on that rate and the number of packets for which we have + * information. The state is a 32-bit unsigned integer in which two + * bits represent a packet: 11 if it went through well, 10 if it went + * through with one retry, 01 if it went through with more than one + * retry, or 00 if it didn't go through at all. We define the + * "goodness" for a particular (rate, direction) combination as the + * sum of all the 2-bit fields, times 33, divided by the number of + * 2-bit fields containing valid information (16 except when we're + * starting out). The number produced is between 0 and 99; we use -1 + * for rates with less than 4 RX packets or 1 TX, as an indicator that + * we do not have enough information to rely on them. + * + * In deciding which rates are best, we find the weighted average of + * TX and RX goodness, where the weighting is by number of packets + * with data and TX packets are worth 4 times as much as RX packets. + * The weighted average is called "net goodness" and is also a number + * between 0 and 99. If 3 consecutive packets fail transmission + * outright, we automatically ratchet down the rate; otherwise, we + * switch to the best rate whenever the current rate's goodness falls + * below some threshold, and try increasing our rate when the goodness + * is very high. + * + * This system is optimized for gPXE's style of usage. Because normal + * operation always involves receiving something, we'll make our way + * to the best rate pretty quickly. We tend to follow the lead of the + * sending AP in choosing rates, but we won't use rates for long that + * don't work well for us in transmission. We assume gPXE won't be + * running for long enough that rate patterns will change much, so we + * don't have to keep time counters or the like. And if this doesn't + * work well in practice there are many ways it could be tweaked. + * + * To avoid staying at 1Mbps for a long time, we don't track any + * transmitted packets until we've set our rate based on received + * packets. + */ + +/** Two-bit packet status indicator for a packet with no retries */ +#define RC_PKT_OK 0x3 + +/** Two-bit packet status indicator for a packet with one retry */ +#define RC_PKT_RETRIED_ONCE 0x2 + +/** Two-bit packet status indicator for a TX packet with multiple retries + * + * It is not possible to tell whether an RX packet had one or multiple + * retries; we rely instead on the fact that failed RX packets won't + * get to us at all, so if we receive a lot of RX packets on a certain + * rate it must be pretty good. + */ +#define RC_PKT_RETRIED_MULTI 0x1 + +/** Two-bit packet status indicator for a TX packet that was never ACKed + * + * It is not possible to tell whether an RX packet was setn if it + * didn't get through to us, but if we don't see one we won't increase + * the goodness for its rate. This asymmetry is part of why TX packets + * are weighted much more heavily than RX. + */ +#define RC_PKT_FAILED 0x0 + +/** Number of times to weight TX packets more heavily than RX packets */ +#define RC_TX_FACTOR 4 + +/** Number of consecutive failed TX packets that cause an automatic rate drop */ +#define RC_TX_EMERG_FAIL 3 + +/** Minimum net goodness below which we will search for a better rate */ +#define RC_GOODNESS_MIN 85 + +/** Maximum net goodness above which we will try to increase our rate */ +#define RC_GOODNESS_MAX 95 + +/** Minimum (num RX + @c RC_TX_FACTOR * num TX) to use a certain rate */ +#define RC_UNCERTAINTY_THRESH 4 + +/** TX direction */ +#define TX 0 + +/** RX direction */ +#define RX 1 + +/** A rate control context */ +struct rc80211_ctx +{ + /** Goodness state for each rate, TX and RX */ + u32 goodness[2][NET80211_MAX_RATES]; + + /** Number of packets recorded for each rate */ + u8 count[2][NET80211_MAX_RATES]; + + /** Indication of whether we've set the device rate yet */ + int started; + + /** Counter of all packets sent and received */ + int packets; +}; + +/** + * Initialize rate-control algorithm + * + * @v dev 802.11 device + * @ret ctx Rate-control context, to be stored in @c dev->rctl + */ +struct rc80211_ctx * rc80211_init ( struct net80211_device *dev __unused ) +{ + struct rc80211_ctx *ret = zalloc ( sizeof ( *ret ) ); + return ret; +} + +/** + * Calculate net goodness for a certain rate + * + * @v ctx Rate-control context + * @v rate_idx Index of rate to calculate net goodness for + */ +static int rc80211_calc_net_goodness ( struct rc80211_ctx *ctx, + int rate_idx ) +{ + int sum[2], num[2], dir, pkt; + + for ( dir = 0; dir < 2; dir++ ) { + u32 good = ctx->goodness[dir][rate_idx]; + + num[dir] = ctx->count[dir][rate_idx]; + sum[dir] = 0; + + for ( pkt = 0; pkt < num[dir]; pkt++ ) + sum[dir] += ( good >> ( 2 * pkt ) ) & 0x3; + } + + if ( ( num[TX] * RC_TX_FACTOR + num[RX] ) < RC_UNCERTAINTY_THRESH ) + return -1; + + return ( 33 * ( sum[TX] * RC_TX_FACTOR + sum[RX] ) / + ( num[TX] * RC_TX_FACTOR + num[RX] ) ); +} + +/** + * Determine the best rate to switch to and return it + * + * @v dev 802.11 device + * @ret rate_idx Index of the best rate to switch to + */ +static int rc80211_pick_best ( struct net80211_device *dev ) +{ + struct rc80211_ctx *ctx = dev->rctl; + int best_net_good = 0, best_rate = -1, i; + + for ( i = 0; i < dev->nr_rates; i++ ) { + int net_good = rc80211_calc_net_goodness ( ctx, i ); + + if ( net_good > best_net_good || + ( best_net_good > RC_GOODNESS_MIN && + net_good > RC_GOODNESS_MIN ) ) { + best_net_good = net_good; + best_rate = i; + } + } + + if ( best_rate >= 0 ) { + int old_good = rc80211_calc_net_goodness ( ctx, dev->rate ); + if ( old_good != best_net_good ) + DBGC ( ctx, "802.11 RC %p switching from goodness " + "%d to %d\n", ctx, old_good, best_net_good ); + + ctx->started = 1; + return best_rate; + } + + return dev->rate; +} + +/** + * Set 802.11 device rate + * + * @v dev 802.11 device + * @v rate_idx Index of rate to switch to + * + * This is a thin wrapper around net80211_set_rate_idx to insert a + * debugging message where appropriate. + */ +static inline void rc80211_set_rate ( struct net80211_device *dev, + int rate_idx ) +{ + DBGC ( dev->rctl, "802.11 RC %p changing rate %d->%d Mbps\n", dev->rctl, + dev->rates[dev->rate] / 10, dev->rates[rate_idx] / 10 ); + + net80211_set_rate_idx ( dev, rate_idx ); +} + +/** + * Check rate-control state and change rate if necessary + * + * @v dev 802.11 device + */ +static void rc80211_maybe_set_new ( struct net80211_device *dev ) +{ + struct rc80211_ctx *ctx = dev->rctl; + int net_good; + + net_good = rc80211_calc_net_goodness ( ctx, dev->rate ); + + if ( ! ctx->started ) { + rc80211_set_rate ( dev, rc80211_pick_best ( dev ) ); + return; + } + + if ( net_good < 0 ) /* insufficient data */ + return; + + if ( net_good > RC_GOODNESS_MAX && dev->rate + 1 < dev->nr_rates ) { + int higher = rc80211_calc_net_goodness ( ctx, dev->rate + 1 ); + if ( higher > net_good || higher < 0 ) + rc80211_set_rate ( dev, dev->rate + 1 ); + else + rc80211_set_rate ( dev, rc80211_pick_best ( dev ) ); + } + + if ( net_good < RC_GOODNESS_MIN ) { + rc80211_set_rate ( dev, rc80211_pick_best ( dev ) ); + } +} + +/** + * Update rate-control state + * + * @v dev 802.11 device + * @v direction One of the direction constants TX or RX + * @v rate_idx Index of rate at which packet was sent or received + * @v retries Number of times packet was retried before success + * @v failed If nonzero, the packet failed to get through + */ +static void rc80211_update ( struct net80211_device *dev, int direction, + int rate_idx, int retries, int failed ) +{ + struct rc80211_ctx *ctx = dev->rctl; + u32 goodness = ctx->goodness[direction][rate_idx]; + + if ( ctx->count[direction][rate_idx] < 16 ) + ctx->count[direction][rate_idx]++; + + goodness <<= 2; + if ( failed ) + goodness |= RC_PKT_FAILED; + else if ( retries > 1 ) + goodness |= RC_PKT_RETRIED_MULTI; + else if ( retries ) + goodness |= RC_PKT_RETRIED_ONCE; + else + goodness |= RC_PKT_OK; + + ctx->goodness[direction][rate_idx] = goodness; + + ctx->packets++; + + rc80211_maybe_set_new ( dev ); +} + +/** + * Update rate-control state for transmitted packet + * + * @v dev 802.11 device + * @v retries Number of times packet was transmitted before success + * @v rc Return status code for transmission + */ +void rc80211_update_tx ( struct net80211_device *dev, int retries, int rc ) +{ + struct rc80211_ctx *ctx = dev->rctl; + + if ( ! ctx->started ) + return; + + rc80211_update ( dev, TX, dev->rate, retries, rc ); + + /* Check if the last RC_TX_EMERG_FAIL packets have all failed */ + if ( ! ( ctx->goodness[TX][dev->rate] & + ( ( 1 << ( 2 * RC_TX_EMERG_FAIL ) ) - 1 ) ) ) { + if ( dev->rate == 0 ) + DBGC ( dev->rctl, "802.11 RC %p saw %d consecutive " + "failed TX, but cannot lower rate any further\n", + dev->rctl, RC_TX_EMERG_FAIL ); + else { + DBGC ( dev->rctl, "802.11 RC %p lowering rate (%d->%d " + "Mbps) due to %d consecutive TX failures\n", + dev->rctl, dev->rates[dev->rate] / 10, + dev->rates[dev->rate - 1] / 10, + RC_TX_EMERG_FAIL ); + + rc80211_set_rate ( dev, dev->rate - 1 ); + } + } +} + +/** + * Update rate-control state for received packet + * + * @v dev 802.11 device + * @v retry Whether the received packet had been retransmitted + * @v rate Rate at which packet was received, in 100 kbps units + */ +void rc80211_update_rx ( struct net80211_device *dev, int retry, u16 rate ) +{ + int ridx; + + for ( ridx = 0; ridx < dev->nr_rates && dev->rates[ridx] != rate; + ridx++ ) + ; + if ( ridx >= dev->nr_rates ) + return; /* couldn't find the rate */ + + rc80211_update ( dev, RX, ridx, retry, 0 ); +} + +/** + * Free rate-control context + * + * @v ctx Rate-control context + */ +void rc80211_free ( struct rc80211_ctx *ctx ) +{ + free ( ctx ); +} |