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Improve performance of the Sample rate algorithm on 802.11n networks.

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* Don't treat high percentage failures as "sucessive failures" - high
  MCS rates are very picky and will quite happily "fade" from low
  to high failure % and back again within a few seconds.  If they really
  don't work, the aggregate will just plain fail.

* Only sample MCS rates +/- 3 from the current MCS.  Sample will back off
  quite quickly, so there's no need to sample _all_ MCS rates between
  a high MCS rate and MCS0; there may be a lot of them.

* Modify the smoothing rate to be 75% rather than 95% - it's more adaptive
  but it comes with a cost of being slightly less stable at times.
  A per-node, hysterisis behaviour would be nicer.
This commit is contained in:
Adrian Chadd 2012-09-17 01:09:17 +00:00
parent d8c4c83314
commit e69db8df7d
1 changed files with 5 additions and 15 deletions
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20
sys/dev/ath/ath_rate/sample/sample.c
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@ -293,27 +293,17 @@ pick_sample_rate(struct sample_softc *ssc , struct ath_node *an,
}
/*
* When doing aggregation, successive failures don't happen
* as often, as sometimes some of the sub-frames get through.
*
* If the sample rix average tx time is greater than the
* average tx time of the current rix, don't immediately use
* the rate for sampling.
* For HT, only sample a few rates on either side of the
* current rix; there's quite likely a lot of them.
*/
if (an->an_node.ni_flags & IEEE80211_NODE_HT) {
if ((sn->stats[size_bin][rix].average_tx_time * 10 >
sn->stats[size_bin][current_rix].average_tx_time * 9) &&
(ticks - sn->stats[size_bin][rix].last_tx < ssc->stale_failure_timeout)) {
if (rix < (current_rix - 3) ||
rix > (current_rix + 3)) {
mask &= ~((uint64_t) 1<<rix);
goto nextrate;
}
}
/*
* XXX TODO
* For HT, limit sample somehow?
*/
/* Don't sample more than 2 rates higher for rates > 11M for non-HT rates */
if (! (an->an_node.ni_flags & IEEE80211_NODE_HT)) {
if (DOT11RATE(rix) > 2*11 && rix > current_rix + 2) {
@ -1420,7 +1410,7 @@ ath_rate_attach(struct ath_softc *sc)
if (ssc == NULL)
return NULL;
ssc->arc.arc_space = sizeof(struct sample_node);
ssc->smoothing_rate = 95; /* ewma percentage ([0..99]) */
ssc->smoothing_rate = 75; /* ewma percentage ([0..99]) */
ssc->smoothing_minpackets = 100 / (100 - ssc->smoothing_rate);
ssc->sample_rate = 10; /* %time to try diff tx rates */
ssc->max_successive_failures = 3; /* threshold for rate sampling*/