Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=2bdc7031f9ea1826e16bffc3540d05de891c98bc
Commit: 2bdc7031f9ea1826e16bffc3540d05de891c98bc
Parent: 529699815b79f15a6644786dc4d6e9dd5153a447
Author: Ben Cahill <[EMAIL PROTECTED]>
AuthorDate: Thu Nov 29 11:10:12 2007 +0800
Committer: David S. Miller <[EMAIL PROTECTED]>
CommitDate: Mon Jan 28 15:05:35 2008 -0800
iwlwifi: document 4965 rate scaling
Document 4965 rate scaling
Signed-off-by: Ben Cahill <[EMAIL PROTECTED]>
Signed-off-by: Zhu Yi <[EMAIL PROTECTED]>
Signed-off-by: John W. Linville <[EMAIL PROTECTED]>
---
drivers/net/wireless/iwlwifi/iwl-4965-commands.h | 251 +++++++++++++++++++++-
1 files changed, 247 insertions(+), 4 deletions(-)
diff --git a/drivers/net/wireless/iwlwifi/iwl-4965-commands.h
b/drivers/net/wireless/iwlwifi/iwl-4965-commands.h
index cbe91db..7988c75 100644
--- a/drivers/net/wireless/iwlwifi/iwl-4965-commands.h
+++ b/drivers/net/wireless/iwlwifi/iwl-4965-commands.h
@@ -1322,6 +1322,8 @@ struct iwl4965_compressed_ba_resp {
/*
* REPLY_TX_PWR_TABLE_CMD = 0x97 (command, has simple generic response)
+ *
+ * See details under "TXPOWER" in iwl-4965-hw.h.
*/
struct iwl4965_txpowertable_cmd {
u8 band; /* 0: 5 GHz, 1: 2.4 GHz */
@@ -1333,39 +1335,280 @@ struct iwl4965_txpowertable_cmd {
/*RS_NEW_API: only TLC_RTS remains and moved to bit 0 */
#define LINK_QUAL_FLAGS_SET_STA_TLC_RTS_MSK (1<<0)
+/* # of EDCA prioritized tx fifos */
#define LINK_QUAL_AC_NUM AC_NUM
+
+/* # entries in rate scale table to support Tx retries */
#define LINK_QUAL_MAX_RETRY_NUM 16
+/* Tx antenna selection values */
#define LINK_QUAL_ANT_A_MSK (1<<0)
#define LINK_QUAL_ANT_B_MSK (1<<1)
#define LINK_QUAL_ANT_MSK (LINK_QUAL_ANT_A_MSK|LINK_QUAL_ANT_B_MSK)
+
+/**
+ * struct iwl4965_link_qual_general_params
+ *
+ * Used in REPLY_TX_LINK_QUALITY_CMD
+ */
struct iwl4965_link_qual_general_params {
u8 flags;
+
+ /* No entries at or above this (driver chosen) index contain MIMO */
u8 mimo_delimiter;
- u8 single_stream_ant_msk;
- u8 dual_stream_ant_msk;
+
+ /* Best single antenna to use for single stream (legacy, SISO). */
+ u8 single_stream_ant_msk; /* LINK_QUAL_ANT_* */
+
+ /* Best antennas to use for MIMO (unused for 4965, assumes both). */
+ u8 dual_stream_ant_msk; /* LINK_QUAL_ANT_* */
+
+ /*
+ * If driver needs to use different initial rates for different
+ * EDCA QOS access categories (as implemented by tx fifos 0-3),
+ * this table will set that up, by indicating the indexes in the
+ * rs_table[LINK_QUAL_MAX_RETRY_NUM] rate table at which to start.
+ * Otherwise, driver should set all entries to 0.
+ *
+ * Entry usage:
+ * 0 = Background, 1 = Best Effort (normal), 2 = Video, 3 = Voice
+ * TX FIFOs above 3 use same value (typically 0) as TX FIFO 3.
+ */
u8 start_rate_index[LINK_QUAL_AC_NUM];
} __attribute__ ((packed));
+/**
+ * struct iwl4965_link_qual_agg_params
+ *
+ * Used in REPLY_TX_LINK_QUALITY_CMD
+ */
struct iwl4965_link_qual_agg_params {
+
+ /* Maximum number of uSec in aggregation.
+ * Driver should set this to 4000 (4 milliseconds). */
__le16 agg_time_limit;
+
+ /*
+ * Number of Tx retries allowed for a frame, before that frame will
+ * no longer be considered for the start of an aggregation sequence
+ * (scheduler will then try to tx it as single frame).
+ * Driver should set this to 3.
+ */
u8 agg_dis_start_th;
+
+ /*
+ * Maximum number of frames in aggregation.
+ * 0 = no limit (default). 1 = no aggregation.
+ * Other values = max # frames in aggregation.
+ */
u8 agg_frame_cnt_limit;
+
__le32 reserved;
} __attribute__ ((packed));
/*
* REPLY_TX_LINK_QUALITY_CMD = 0x4e (command, has simple generic response)
+ *
+ * For 4965 only; 3945 uses REPLY_RATE_SCALE.
+ *
+ * Each station in the 4965's internal station table has its own table of 16
+ * Tx rates and modulation modes (e.g. legacy/SISO/MIMO) for retrying Tx when
+ * an ACK is not received. This command replaces the entire table for
+ * one station.
+ *
+ * NOTE: Station must already be in 4965's station table. Use REPLY_ADD_STA.
+ *
+ * The rate scaling procedures described below work well. Of course, other
+ * procedures are possible, and may work better for particular environments.
+ *
+ *
+ * FILLING THE RATE TABLE
+ *
+ * Given a particular initial rate and mode, as determined by the rate
+ * scaling algorithm described below, the Linux driver uses the following
+ * formula to fill the rs_table[LINK_QUAL_MAX_RETRY_NUM] rate table in the
+ * Link Quality command:
+ *
+ *
+ * 1) If using High-throughput (HT) (SISO or MIMO) initial rate:
+ * a) Use this same initial rate for first 3 entries.
+ * b) Find next lower available rate using same mode (SISO or MIMO),
+ * use for next 3 entries. If no lower rate available, switch to
+ * legacy mode (no FAT channel, no MIMO, no short guard interval).
+ * c) If using MIMO, set command's mimo_delimiter to number of entries
+ * using MIMO (3 or 6).
+ * d) After trying 2 HT rates, switch to legacy mode (no FAT channel,
+ * no MIMO, no short guard interval), at the next lower bit rate
+ * (e.g. if second HT bit rate was 54, try 48 legacy), and follow
+ * legacy procedure for remaining table entries.
+ *
+ * 2) If using legacy initial rate:
+ * a) Use the initial rate for only one entry.
+ * b) For each following entry, reduce the rate to next lower available
+ * rate, until reaching the lowest available rate.
+ * c) When reducing rate, also switch antenna selection.
+ * d) Once lowest available rate is reached, repeat this rate until
+ * rate table is filled (16 entries), switching antenna each entry.
+ *
+ *
+ * ACCUMULATING HISTORY
+ *
+ * The rate scaling algorithm for 4965, as implemented in Linux driver, uses
+ * two sets of frame Tx success history: One for the current/active modulation
+ * mode, and one for a speculative/search mode that is being attempted. If the
+ * speculative mode turns out to be more effective (i.e. actual transfer
+ * rate is better), then the driver continues to use the speculative mode
+ * as the new current active mode.
+ *
+ * Each history set contains, separately for each possible rate, data for a
+ * sliding window of the 62 most recent tx attempts at that rate. The data
+ * includes a shifting bitmap of success(1)/failure(0), and sums of successful
+ * and attempted frames, from which the driver can additionally calculate a
+ * success ratio (success / attempted) and number of failures
+ * (attempted - success), and control the size of the window (attempted).
+ * The driver uses the bit map to remove successes from the success sum, as
+ * the oldest tx attempts fall out of the window.
+ *
+ * When the 4965 makes multiple tx attempts for a given frame, each attempt
+ * might be at a different rate, and have different modulation characteristics
+ * (e.g. antenna, fat channel, short guard interval), as set up in the rate
+ * scaling table in the Link Quality command. The driver must determine
+ * which rate table entry was used for each tx attempt, to determine which
+ * rate-specific history to update, and record only those attempts that
+ * match the modulation characteristics of the history set.
+ *
+ * When using block-ack (aggregation), all frames are transmitted at the same
+ * rate, since there is no per-attempt acknowledgement from the destination
+ * station. The Tx response struct iwl_tx_resp indicates the Tx rate in
+ * rate_n_flags field. After receiving a block-ack, the driver can update
+ * history for the entire block all at once.
+ *
+ *
+ * FINDING BEST STARTING RATE:
+ *
+ * When working with a selected initial modulation mode (see below), the
+ * driver attempts to find a best initial rate. The initial rate is the
+ * first entry in the Link Quality command's rate table.
+ *
+ * 1) Calculate actual throughput (success ratio * expected throughput, see
+ * table below) for current initial rate. Do this only if enough frames
+ * have been attempted to make the value meaningful: at least 6 failed
+ * tx attempts, or at least 8 successes. If not enough, don't try rate
+ * scaling yet.
+ *
+ * 2) Find available rates adjacent to current initial rate. Available means:
+ * a) supported by hardware &&
+ * b) supported by association &&
+ * c) within any constraints selected by user
+ *
+ * 3) Gather measured throughputs for adjacent rates. These might not have
+ * enough history to calculate a throughput. That's okay, we might try
+ * using one of them anyway!
+ *
+ * 4) Try decreasing rate if, for current rate:
+ * a) success ratio is < 15% ||
+ * b) lower adjacent rate has better measured throughput ||
+ * c) higher adjacent rate has worse throughput, and lower is unmeasured
+ *
+ * As a sanity check, if decrease was determined above, leave rate
+ * unchanged if:
+ * a) lower rate unavailable
+ * b) success ratio at current rate > 85% (very good)
+ * c) current measured throughput is better than expected throughput
+ * of lower rate (under perfect 100% tx conditions, see table below)
+ *
+ * 5) Try increasing rate if, for current rate:
+ * a) success ratio is < 15% ||
+ * b) both adjacent rates' throughputs are unmeasured (try it!) ||
+ * b) higher adjacent rate has better measured throughput ||
+ * c) lower adjacent rate has worse throughput, and higher is unmeasured
+ *
+ * As a sanity check, if increase was determined above, leave rate
+ * unchanged if:
+ * a) success ratio at current rate < 70%. This is not particularly
+ * good performance; higher rate is sure to have poorer success.
+ *
+ * 6) Re-evaluate the rate after each tx frame. If working with block-
+ * acknowledge, history and statistics may be calculated for the entire
+ * block (including prior history that fits within the history windows),
+ * before re-evaluation.
+ *
+ * FINDING BEST STARTING MODULATION MODE:
+ *
+ * After working with a modulation mode for a "while" (and doing rate scaling),
+ * the driver searches for a new initial mode in an attempt to improve
+ * throughput. The "while" is measured by numbers of attempted frames:
+ *
+ * For legacy mode, search for new mode after:
+ * 480 successful frames, or 160 failed frames
+ * For high-throughput modes (SISO or MIMO), search for new mode after:
+ * 4500 successful frames, or 400 failed frames
+ *
+ * Mode switch possibilities are (3 for each mode):
+ *
+ * For legacy:
+ * Change antenna, try SISO (if HT association), try MIMO (if HT association)
+ * For SISO:
+ * Change antenna, try MIMO, try shortened guard interval (SGI)
+ * For MIMO:
+ * Try SISO antenna A, SISO antenna B, try shortened guard interval (SGI)
+ *
+ * When trying a new mode, use the same bit rate as the old/current mode when
+ * trying antenna switches and shortened guard interval. When switching to
+ * SISO from MIMO or legacy, or to MIMO from SISO or legacy, use a rate
+ * for which the expected throughput (under perfect conditions) is about the
+ * same or slightly better than the actual measured throughput delivered by
+ * the old/current mode.
+ *
+ * Actual throughput can be estimated by multiplying the expected throughput
+ * by the success ratio (successful / attempted tx frames). Frame size is
+ * not considered in this calculation; it assumes that frame size will average
+ * out to be fairly consistent over several samples. The following are
+ * metric values for expected throughput assuming 100% success ratio.
+ * Only G band has support for CCK rates:
+ *
+ * RATE: 1 2 5 11 6 9 12 18 24 36 48 54
60
+ *
+ * G: 7 13 35 58 40 57 72 98 121 154 177 186
186
+ * A: 0 0 0 0 40 57 72 98 121 154 177 186
186
+ * SISO 20MHz: 0 0 0 0 42 42 76 102 124 159 183 193
202
+ * SGI SISO 20MHz: 0 0 0 0 46 46 82 110 132 168 192 202
211
+ * MIMO 20MHz: 0 0 0 0 74 74 123 155 179 214 236 244
251
+ * SGI MIMO 20MHz: 0 0 0 0 81 81 131 164 188 222 243 251
257
+ * SISO 40MHz: 0 0 0 0 77 77 127 160 184 220 242 250
257
+ * SGI SISO 40MHz: 0 0 0 0 83 83 135 169 193 229 250 257
264
+ * MIMO 40MHz: 0 0 0 0 123 123 182 214 235 264 279 285
289
+ * SGI MIMO 40MHz: 0 0 0 0 131 131 191 222 242 270 284 289
293
+ *
+ * After the new mode has been tried for a short while (minimum of 6 failed
+ * frames or 8 successful frames), compare success ratio and actual throughput
+ * estimate of the new mode with the old. If either is better with the new
+ * mode, continue to use the new mode.
+ *
+ * Continue comparing modes until all 3 possibilities have been tried.
+ * If moving from legacy to HT, try all 3 possibilities from the new HT
+ * mode. After trying all 3, a best mode is found. Continue to use this mode
+ * for the longer "while" described above (e.g. 480 successful frames for
+ * legacy), and then repeat the search process.
+ *
*/
struct iwl4965_link_quality_cmd {
+
+ /* Index of destination/recipient station in uCode's station table */
u8 sta_id;
u8 reserved1;
- __le16 control;
+ __le16 control; /* not used */
struct iwl4965_link_qual_general_params general_params;
struct iwl4965_link_qual_agg_params agg_params;
+
+ /*
+ * Rate info; when using rate-scaling, Tx command's initial_rate_index
+ * specifies 1st Tx rate attempted, via index into this table.
+ * 4965 works its way through table when retrying Tx.
+ */
struct {
- __le32 rate_n_flags;
+ __le32 rate_n_flags; /* RATE_MCS_*, IWL_RATE_* */
} rs_table[LINK_QUAL_MAX_RETRY_NUM];
__le32 reserved2;
} __attribute__ ((packed));
-
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