iwlwifi: document 4965 rate scaling
Document 4965 rate scaling Signed-off-by: Ben Cahill <ben.m.cahill@intel.com> Signed-off-by: Zhu Yi <yi.zhu@intel.com> Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Ben Cahill
David S. Miller
parent
529699815b
commit
2bdc7031f9
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@ -1322,6 +1322,8 @@ struct iwl4965_compressed_ba_resp {
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/*
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* REPLY_TX_PWR_TABLE_CMD = 0x97 (command, has simple generic response)
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*
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* See details under "TXPOWER" in iwl-4965-hw.h.
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*/
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struct iwl4965_txpowertable_cmd {
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u8 band; /* 0: 5 GHz, 1: 2.4 GHz */
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@ -1333,39 +1335,280 @@ struct iwl4965_txpowertable_cmd {
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/*RS_NEW_API: only TLC_RTS remains and moved to bit 0 */
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#define LINK_QUAL_FLAGS_SET_STA_TLC_RTS_MSK (1<<0)
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/* # of EDCA prioritized tx fifos */
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#define LINK_QUAL_AC_NUM AC_NUM
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/* # entries in rate scale table to support Tx retries */
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#define LINK_QUAL_MAX_RETRY_NUM 16
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/* Tx antenna selection values */
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#define LINK_QUAL_ANT_A_MSK (1<<0)
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#define LINK_QUAL_ANT_B_MSK (1<<1)
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#define LINK_QUAL_ANT_MSK (LINK_QUAL_ANT_A_MSK|LINK_QUAL_ANT_B_MSK)
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/**
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* struct iwl4965_link_qual_general_params
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*
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* Used in REPLY_TX_LINK_QUALITY_CMD
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*/
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struct iwl4965_link_qual_general_params {
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u8 flags;
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/* No entries at or above this (driver chosen) index contain MIMO */
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u8 mimo_delimiter;
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u8 single_stream_ant_msk;
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u8 dual_stream_ant_msk;
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/* Best single antenna to use for single stream (legacy, SISO). */
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u8 single_stream_ant_msk; /* LINK_QUAL_ANT_* */
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/* Best antennas to use for MIMO (unused for 4965, assumes both). */
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u8 dual_stream_ant_msk; /* LINK_QUAL_ANT_* */
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/*
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* If driver needs to use different initial rates for different
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* EDCA QOS access categories (as implemented by tx fifos 0-3),
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* this table will set that up, by indicating the indexes in the
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* rs_table[LINK_QUAL_MAX_RETRY_NUM] rate table at which to start.
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* Otherwise, driver should set all entries to 0.
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*
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* Entry usage:
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* 0 = Background, 1 = Best Effort (normal), 2 = Video, 3 = Voice
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* TX FIFOs above 3 use same value (typically 0) as TX FIFO 3.
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*/
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u8 start_rate_index[LINK_QUAL_AC_NUM];
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} __attribute__ ((packed));
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/**
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* struct iwl4965_link_qual_agg_params
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*
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* Used in REPLY_TX_LINK_QUALITY_CMD
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*/
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struct iwl4965_link_qual_agg_params {
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/* Maximum number of uSec in aggregation.
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* Driver should set this to 4000 (4 milliseconds). */
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__le16 agg_time_limit;
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/*
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* Number of Tx retries allowed for a frame, before that frame will
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* no longer be considered for the start of an aggregation sequence
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* (scheduler will then try to tx it as single frame).
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* Driver should set this to 3.
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*/
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u8 agg_dis_start_th;
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/*
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* Maximum number of frames in aggregation.
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* 0 = no limit (default). 1 = no aggregation.
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* Other values = max # frames in aggregation.
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*/
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u8 agg_frame_cnt_limit;
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__le32 reserved;
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} __attribute__ ((packed));
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/*
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* REPLY_TX_LINK_QUALITY_CMD = 0x4e (command, has simple generic response)
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*
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* For 4965 only; 3945 uses REPLY_RATE_SCALE.
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*
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* Each station in the 4965's internal station table has its own table of 16
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* Tx rates and modulation modes (e.g. legacy/SISO/MIMO) for retrying Tx when
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* an ACK is not received. This command replaces the entire table for
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* one station.
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*
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* NOTE: Station must already be in 4965's station table. Use REPLY_ADD_STA.
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*
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* The rate scaling procedures described below work well. Of course, other
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* procedures are possible, and may work better for particular environments.
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*
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*
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* FILLING THE RATE TABLE
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*
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* Given a particular initial rate and mode, as determined by the rate
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* scaling algorithm described below, the Linux driver uses the following
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* formula to fill the rs_table[LINK_QUAL_MAX_RETRY_NUM] rate table in the
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* Link Quality command:
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*
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*
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* 1) If using High-throughput (HT) (SISO or MIMO) initial rate:
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* a) Use this same initial rate for first 3 entries.
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* b) Find next lower available rate using same mode (SISO or MIMO),
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* use for next 3 entries. If no lower rate available, switch to
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* legacy mode (no FAT channel, no MIMO, no short guard interval).
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* c) If using MIMO, set command's mimo_delimiter to number of entries
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* using MIMO (3 or 6).
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* d) After trying 2 HT rates, switch to legacy mode (no FAT channel,
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* no MIMO, no short guard interval), at the next lower bit rate
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* (e.g. if second HT bit rate was 54, try 48 legacy), and follow
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* legacy procedure for remaining table entries.
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*
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* 2) If using legacy initial rate:
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* a) Use the initial rate for only one entry.
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* b) For each following entry, reduce the rate to next lower available
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* rate, until reaching the lowest available rate.
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* c) When reducing rate, also switch antenna selection.
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* d) Once lowest available rate is reached, repeat this rate until
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* rate table is filled (16 entries), switching antenna each entry.
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*
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*
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* ACCUMULATING HISTORY
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*
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* The rate scaling algorithm for 4965, as implemented in Linux driver, uses
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* two sets of frame Tx success history: One for the current/active modulation
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* mode, and one for a speculative/search mode that is being attempted. If the
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* speculative mode turns out to be more effective (i.e. actual transfer
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* rate is better), then the driver continues to use the speculative mode
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* as the new current active mode.
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*
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* Each history set contains, separately for each possible rate, data for a
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* sliding window of the 62 most recent tx attempts at that rate. The data
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* includes a shifting bitmap of success(1)/failure(0), and sums of successful
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* and attempted frames, from which the driver can additionally calculate a
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* success ratio (success / attempted) and number of failures
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* (attempted - success), and control the size of the window (attempted).
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* The driver uses the bit map to remove successes from the success sum, as
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* the oldest tx attempts fall out of the window.
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*
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* When the 4965 makes multiple tx attempts for a given frame, each attempt
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* might be at a different rate, and have different modulation characteristics
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* (e.g. antenna, fat channel, short guard interval), as set up in the rate
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* scaling table in the Link Quality command. The driver must determine
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* which rate table entry was used for each tx attempt, to determine which
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* rate-specific history to update, and record only those attempts that
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* match the modulation characteristics of the history set.
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*
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* When using block-ack (aggregation), all frames are transmitted at the same
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* rate, since there is no per-attempt acknowledgement from the destination
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* station. The Tx response struct iwl_tx_resp indicates the Tx rate in
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* rate_n_flags field. After receiving a block-ack, the driver can update
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* history for the entire block all at once.
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*
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*
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* FINDING BEST STARTING RATE:
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*
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* When working with a selected initial modulation mode (see below), the
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* driver attempts to find a best initial rate. The initial rate is the
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* first entry in the Link Quality command's rate table.
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*
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* 1) Calculate actual throughput (success ratio * expected throughput, see
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* table below) for current initial rate. Do this only if enough frames
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* have been attempted to make the value meaningful: at least 6 failed
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* tx attempts, or at least 8 successes. If not enough, don't try rate
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* scaling yet.
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*
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* 2) Find available rates adjacent to current initial rate. Available means:
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* a) supported by hardware &&
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* b) supported by association &&
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* c) within any constraints selected by user
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*
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* 3) Gather measured throughputs for adjacent rates. These might not have
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* enough history to calculate a throughput. That's okay, we might try
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* using one of them anyway!
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*
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* 4) Try decreasing rate if, for current rate:
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* a) success ratio is < 15% ||
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* b) lower adjacent rate has better measured throughput ||
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* c) higher adjacent rate has worse throughput, and lower is unmeasured
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*
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* As a sanity check, if decrease was determined above, leave rate
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* unchanged if:
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* a) lower rate unavailable
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* b) success ratio at current rate > 85% (very good)
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* c) current measured throughput is better than expected throughput
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* of lower rate (under perfect 100% tx conditions, see table below)
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*
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* 5) Try increasing rate if, for current rate:
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* a) success ratio is < 15% ||
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* b) both adjacent rates' throughputs are unmeasured (try it!) ||
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* b) higher adjacent rate has better measured throughput ||
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* c) lower adjacent rate has worse throughput, and higher is unmeasured
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*
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* As a sanity check, if increase was determined above, leave rate
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* unchanged if:
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* a) success ratio at current rate < 70%. This is not particularly
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* good performance; higher rate is sure to have poorer success.
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*
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* 6) Re-evaluate the rate after each tx frame. If working with block-
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* acknowledge, history and statistics may be calculated for the entire
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* block (including prior history that fits within the history windows),
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* before re-evaluation.
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*
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* FINDING BEST STARTING MODULATION MODE:
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*
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* After working with a modulation mode for a "while" (and doing rate scaling),
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* the driver searches for a new initial mode in an attempt to improve
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* throughput. The "while" is measured by numbers of attempted frames:
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*
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* For legacy mode, search for new mode after:
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* 480 successful frames, or 160 failed frames
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* For high-throughput modes (SISO or MIMO), search for new mode after:
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* 4500 successful frames, or 400 failed frames
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*
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* Mode switch possibilities are (3 for each mode):
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*
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* For legacy:
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* Change antenna, try SISO (if HT association), try MIMO (if HT association)
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* For SISO:
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* Change antenna, try MIMO, try shortened guard interval (SGI)
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* For MIMO:
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* Try SISO antenna A, SISO antenna B, try shortened guard interval (SGI)
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*
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* When trying a new mode, use the same bit rate as the old/current mode when
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* trying antenna switches and shortened guard interval. When switching to
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* SISO from MIMO or legacy, or to MIMO from SISO or legacy, use a rate
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* for which the expected throughput (under perfect conditions) is about the
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* same or slightly better than the actual measured throughput delivered by
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* the old/current mode.
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*
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* Actual throughput can be estimated by multiplying the expected throughput
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* by the success ratio (successful / attempted tx frames). Frame size is
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* not considered in this calculation; it assumes that frame size will average
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* out to be fairly consistent over several samples. The following are
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* metric values for expected throughput assuming 100% success ratio.
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* Only G band has support for CCK rates:
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*
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* RATE: 1 2 5 11 6 9 12 18 24 36 48 54 60
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*
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* G: 7 13 35 58 40 57 72 98 121 154 177 186 186
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* A: 0 0 0 0 40 57 72 98 121 154 177 186 186
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* SISO 20MHz: 0 0 0 0 42 42 76 102 124 159 183 193 202
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* SGI SISO 20MHz: 0 0 0 0 46 46 82 110 132 168 192 202 211
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* MIMO 20MHz: 0 0 0 0 74 74 123 155 179 214 236 244 251
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* SGI MIMO 20MHz: 0 0 0 0 81 81 131 164 188 222 243 251 257
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* SISO 40MHz: 0 0 0 0 77 77 127 160 184 220 242 250 257
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* SGI SISO 40MHz: 0 0 0 0 83 83 135 169 193 229 250 257 264
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* MIMO 40MHz: 0 0 0 0 123 123 182 214 235 264 279 285 289
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* SGI MIMO 40MHz: 0 0 0 0 131 131 191 222 242 270 284 289 293
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*
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* After the new mode has been tried for a short while (minimum of 6 failed
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* frames or 8 successful frames), compare success ratio and actual throughput
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* estimate of the new mode with the old. If either is better with the new
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* mode, continue to use the new mode.
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*
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* Continue comparing modes until all 3 possibilities have been tried.
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* If moving from legacy to HT, try all 3 possibilities from the new HT
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* mode. After trying all 3, a best mode is found. Continue to use this mode
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* for the longer "while" described above (e.g. 480 successful frames for
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* legacy), and then repeat the search process.
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*
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*/
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struct iwl4965_link_quality_cmd {
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/* Index of destination/recipient station in uCode's station table */
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u8 sta_id;
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u8 reserved1;
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__le16 control;
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__le16 control; /* not used */
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struct iwl4965_link_qual_general_params general_params;
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struct iwl4965_link_qual_agg_params agg_params;
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/*
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* Rate info; when using rate-scaling, Tx command's initial_rate_index
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* specifies 1st Tx rate attempted, via index into this table.
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* 4965 works its way through table when retrying Tx.
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*/
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struct {
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__le32 rate_n_flags;
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__le32 rate_n_flags; /* RATE_MCS_*, IWL_RATE_* */
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} rs_table[LINK_QUAL_MAX_RETRY_NUM];
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__le32 reserved2;
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} __attribute__ ((packed));
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