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Diffstat (limited to 'gpxe/src/net/80211/rc80211.c')
| -rw-r--r-- | gpxe/src/net/80211/rc80211.c | 371 |
1 files changed, 0 insertions, 371 deletions
diff --git a/gpxe/src/net/80211/rc80211.c b/gpxe/src/net/80211/rc80211.c deleted file mode 100644 index 5bd19143..00000000 --- a/gpxe/src/net/80211/rc80211.c +++ /dev/null @@ -1,371 +0,0 @@ -/* - * 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 ); -} |