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iwlwifi: limit number of attempts for highest HT rate

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When filling out its rate scale table, iwlwifi repeats the first HT rate
IWL_HT_NUMBER_TRY times. The hardware scheduler will stop using
aggregation for any frame that fails LINK_QUAL_AGG_DISABLE_START_DEF
times. Currently, both these constants equal 3.

If iwlwifi probes a faster rate than the link supports, all frames in a
(potentially tens of frames large) batch will fail IWL_HT_NUMBER_TRY
times. Because this happens to be as large as
LINK_QUAL_AGG_DISABLE_START_DEF, all frames will then be sent
individually. This leads to a short, but performance-degrading window
where the legacy stop-and-wait MAC takes over.

Bounding the initial rate by (LINK_QUAL_AGG_DISABLE_START_DEF-1)
attempts makes the third try use a lower rate and hence more be likely
to succeed. This somewhat mitigates the above described behavior.

Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
This commit is contained in:
Daniel Halperin
2011-03-16 19:16:36 -07:00
committed by Wey-Yi Guy
parent c8823ec133
commit 374920cb05
1 changed files with 2 additions and 1 deletions
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3
drivers/net/wireless/iwlwifi/iwl-agn-rs.c
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@@ -2912,7 +2912,8 @@ static void rs_fill_link_cmd(struct iwl_priv *priv,
ant_toggle_cnt = 1;
repeat_rate = IWL_NUMBER_TRY;
} else {
repeat_rate = IWL_HT_NUMBER_TRY;
repeat_rate = min(IWL_HT_NUMBER_TRY,
LINK_QUAL_AGG_DISABLE_START_DEF - 1);
}
lq_cmd->general_params.mimo_delimiter =