Improve 802.11ac throughput on iwm(4) at a distance to the access point.

iwm(4) didn't attribute retries to the correct MCS, resulting in lower
MCS being punished unfairly when a higher MCS kept failing.

Tested by bket, florian, Uwe Werler, and myself.

ok bket

diff --git a/sys/dev/pci/if_iwm.c b/sys/dev/pci/if_iwm.c
index d7abfc1..6de80bd 100644 (file)
--- a/sys/dev/pci/if_iwm.c
+++ b/sys/dev/pci/if_iwm.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: if_iwm.c,v 1.399 2022/03/20 12:01:58 stsp Exp $       */
+/*     $OpenBSD: if_iwm.c,v 1.400 2022/03/23 09:22:49 stsp Exp $       */
 
 /*
  * Copyright (c) 2014, 2016 genua gmbh <info@genua.de>
@@ -5532,6 +5532,8 @@ iwm_vht_single_rate_control(struct iwm_softc *sc, struct ieee80211_node *ni,
 {
        struct ieee80211com *ic = &sc->sc_ic;
        struct iwm_node *in = (void *)ni;
+       uint8_t vht_chan_width = IEEE80211_VHTOP0_CHAN_WIDTH_80;
+       uint8_t sco = IEEE80211_HTOP0_SCO_SCN;
 
        /* Ignore Tx reports which don't match our last LQ command. */
        if (txmcs != ni->ni_txmcs || nss != ni->ni_vht_ss) {
@@ -5544,13 +5546,34 @@ iwm_vht_single_rate_control(struct iwm_softc *sc, struct ieee80211_node *ni,
                int mcs = txmcs;
                unsigned int retries = 0, i;
 
+               if (in->in_phyctxt) {
+                       vht_chan_width = in->in_phyctxt->vht_chan_width;
+                       sco = in->in_phyctxt->sco;
+               }
                in->lq_rate_mismatch = 0;
 
                for (i = 0; i < failure_frame; i++) {
                        if (mcs > 0) {
                                ieee80211_ra_vht_add_stats(&in->in_rn_vht,
                                    ic, ni, mcs, nss, 1, 1);
-                               mcs--;
+                               if (vht_chan_width >=
+                                   IEEE80211_VHTOP0_CHAN_WIDTH_80) {
+                                       /*
+                                        * First 4 Tx attempts used same MCS,
+                                        * twice at 80MHz and twice at 40MHz.
+                                        */
+                                       if (i >= 4)
+                                               mcs--;
+                               } else if (sco == IEEE80211_HTOP0_SCO_SCA ||
+                                   sco == IEEE80211_HTOP0_SCO_SCB) {
+                                       /*
+                                        * First 4 Tx attempts used same MCS,
+                                        * four times at 40MHz.
+                                        */
+                                       if (i >= 4)
+                                               mcs--;
+                               } else
+                                       mcs--;
                        } else
                                retries++;
                }
@@ -9234,7 +9257,7 @@ iwm_set_rate_table_vht(struct iwm_node *in, struct iwm_lq_cmd *lqcmd)
                        }
 
                        /*
-                        * First two Tx attempts may use 80MHz/SGI.
+                        * First two Tx attempts may use 80MHz/40MHz/SGI.
                         * Next two Tx attempts may use 40MHz/SGI.
                         * Beyond that use 20 MHz and decrease the rate.
                         * As a special case, MCS 9 is invalid on 20 Mhz.
@@ -9257,7 +9280,7 @@ iwm_set_rate_table_vht(struct iwm_node *in, struct iwm_lq_cmd *lqcmd)
                                tab |= IWM_RATE_MCS_RTS_REQUIRED_MSK;
                                if (ieee80211_ra_vht_use_sgi(ni))
                                        tab |= IWM_RATE_MCS_SGI_MSK;
-                       } else if (i >= 2 && i < 4 &&
+                       } else if (i < 4 &&
                            in->in_phyctxt->vht_chan_width >=
                            IEEE80211_VHTOP0_CHAN_WIDTH_HT &&
                            (in->in_phyctxt->sco == IEEE80211_HTOP0_SCO_SCA ||