mac80211: minstrel: remove divisions in tx status path

Use a slightly different threshold for downgrading spatial streams to
make it easier to calculate without divisions.
Slightly reduces CPU overhead.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20191008171139.96476-1-nbd@nbd.name
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rc80211_minstrel.c

@@ -289,8 +289,7 @@ minstrel_tx_status(void *priv, struct ieee80211_supported_band *sband,
 	if (mi->sample_deferred > 0)
 		mi->sample_deferred--;
 
-	if (time_after(jiffies, mi->last_stats_update +
-				(mp->update_interval * HZ) / 1000))
+	if (time_after(jiffies, mi->last_stats_update + mp->update_interval))
 		minstrel_update_stats(mp, mi);
 }
 

net/mac80211/rc80211_minstrel_ht.c

@@ -970,23 +970,21 @@ minstrel_ht_tx_status(void *priv, struct ieee80211_supported_band *sband,
 		 */
 		rate = minstrel_get_ratestats(mi, mi->max_tp_rate[0]);
 		if (rate->attempts > 30 &&
-		    MINSTREL_FRAC(rate->success, rate->attempts) <
-		    MINSTREL_FRAC(20, 100)) {
+		    rate->success < rate->attempts / 4) {
 			minstrel_downgrade_rate(mi, &mi->max_tp_rate[0], true);
 			update = true;
 		}
 
 		rate2 = minstrel_get_ratestats(mi, mi->max_tp_rate[1]);
 		if (rate2->attempts > 30 &&
-		    MINSTREL_FRAC(rate2->success, rate2->attempts) <
-		    MINSTREL_FRAC(20, 100)) {
+		    rate2->success < rate2->attempts / 4) {
 			minstrel_downgrade_rate(mi, &mi->max_tp_rate[1], false);
 			update = true;
 		}
 	}
 
 	if (time_after(jiffies, mi->last_stats_update +
-				(mp->update_interval / 2 * HZ) / 1000)) {
+				mp->update_interval / 2)) {
 		update = true;
 		minstrel_ht_update_stats(mp, mi, true);
 	}
@@ -1666,7 +1664,7 @@ minstrel_ht_alloc(struct ieee80211_hw *hw, struct dentry *debugfsdir)
 		mp->has_mrr = true;
 
 	mp->hw = hw;
-	mp->update_interval = 100;
+	mp->update_interval = HZ / 10;
 
 #ifdef CONFIG_MAC80211_DEBUGFS
 	mp->fixed_rate_idx = (u32) -1;