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Subject[PATCH 5.8 077/177] mac80211: reduce packet loss event false positives
Date
From: Felix Fietkau <nbd@nbd.name>

[ Upstream commit 47df8e059b49a80c179fae39256bcd7096810934 ]

When running a large number of packets per second with a high data rate
and long A-MPDUs, the packet loss threshold can be reached very quickly
when the link conditions change. This frequently shows up as spurious
disconnects.
Mitigate false positives by using a similar logic for regular stations
as the one being used for TDLS, though with a more aggressive timeout.
Packet loss events are only reported if no ACK was received for a second.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20200808172542.41628-1-nbd@nbd.name
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/mac80211/sta_info.h | 4 ++--
net/mac80211/status.c | 31 +++++++++++++++----------------
2 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/net/mac80211/sta_info.h b/net/mac80211/sta_info.h
index 49728047dfad6..f66fcce8e6a45 100644
--- a/net/mac80211/sta_info.h
+++ b/net/mac80211/sta_info.h
@@ -522,7 +522,7 @@ struct ieee80211_sta_rx_stats {
* @status_stats.retry_failed: # of frames that failed after retry
* @status_stats.retry_count: # of retries attempted
* @status_stats.lost_packets: # of lost packets
- * @status_stats.last_tdls_pkt_time: timestamp of last TDLS packet
+ * @status_stats.last_pkt_time: timestamp of last ACKed packet
* @status_stats.msdu_retries: # of MSDU retries
* @status_stats.msdu_failed: # of failed MSDUs
* @status_stats.last_ack: last ack timestamp (jiffies)
@@ -595,7 +595,7 @@ struct sta_info {
unsigned long filtered;
unsigned long retry_failed, retry_count;
unsigned int lost_packets;
- unsigned long last_tdls_pkt_time;
+ unsigned long last_pkt_time;
u64 msdu_retries[IEEE80211_NUM_TIDS + 1];
u64 msdu_failed[IEEE80211_NUM_TIDS + 1];
unsigned long last_ack;
diff --git a/net/mac80211/status.c b/net/mac80211/status.c
index cbc40b358ba26..819c4221c284e 100644
--- a/net/mac80211/status.c
+++ b/net/mac80211/status.c
@@ -755,12 +755,16 @@ static void ieee80211_report_used_skb(struct ieee80211_local *local,
* - current throughput (higher value for higher tpt)?
*/
#define STA_LOST_PKT_THRESHOLD 50
+#define STA_LOST_PKT_TIME HZ /* 1 sec since last ACK */
#define STA_LOST_TDLS_PKT_THRESHOLD 10
#define STA_LOST_TDLS_PKT_TIME (10*HZ) /* 10secs since last ACK */

static void ieee80211_lost_packet(struct sta_info *sta,
struct ieee80211_tx_info *info)
{
+ unsigned long pkt_time = STA_LOST_PKT_TIME;
+ unsigned int pkt_thr = STA_LOST_PKT_THRESHOLD;
+
/* If driver relies on its own algorithm for station kickout, skip
* mac80211 packet loss mechanism.
*/
@@ -773,21 +777,20 @@ static void ieee80211_lost_packet(struct sta_info *sta,
return;

sta->status_stats.lost_packets++;
- if (!sta->sta.tdls &&
- sta->status_stats.lost_packets < STA_LOST_PKT_THRESHOLD)
- return;
+ if (sta->sta.tdls) {
+ pkt_time = STA_LOST_TDLS_PKT_TIME;
+ pkt_thr = STA_LOST_PKT_THRESHOLD;
+ }

/*
* If we're in TDLS mode, make sure that all STA_LOST_TDLS_PKT_THRESHOLD
* of the last packets were lost, and that no ACK was received in the
* last STA_LOST_TDLS_PKT_TIME ms, before triggering the CQM packet-loss
* mechanism.
+ * For non-TDLS, use STA_LOST_PKT_THRESHOLD and STA_LOST_PKT_TIME
*/
- if (sta->sta.tdls &&
- (sta->status_stats.lost_packets < STA_LOST_TDLS_PKT_THRESHOLD ||
- time_before(jiffies,
- sta->status_stats.last_tdls_pkt_time +
- STA_LOST_TDLS_PKT_TIME)))
+ if (sta->status_stats.lost_packets < pkt_thr ||
+ !time_after(jiffies, sta->status_stats.last_pkt_time + pkt_time))
return;

cfg80211_cqm_pktloss_notify(sta->sdata->dev, sta->sta.addr,
@@ -1035,9 +1038,7 @@ static void __ieee80211_tx_status(struct ieee80211_hw *hw,
sta->status_stats.lost_packets = 0;

/* Track when last TDLS packet was ACKed */
- if (test_sta_flag(sta, WLAN_STA_TDLS_PEER_AUTH))
- sta->status_stats.last_tdls_pkt_time =
- jiffies;
+ sta->status_stats.last_pkt_time = jiffies;
} else if (noack_success) {
/* nothing to do here, do not account as lost */
} else {
@@ -1170,9 +1171,8 @@ void ieee80211_tx_status_ext(struct ieee80211_hw *hw,
if (sta->status_stats.lost_packets)
sta->status_stats.lost_packets = 0;

- /* Track when last TDLS packet was ACKed */
- if (test_sta_flag(sta, WLAN_STA_TDLS_PEER_AUTH))
- sta->status_stats.last_tdls_pkt_time = jiffies;
+ /* Track when last packet was ACKed */
+ sta->status_stats.last_pkt_time = jiffies;
} else if (test_sta_flag(sta, WLAN_STA_PS_STA)) {
return;
} else if (noack_success) {
@@ -1261,8 +1261,7 @@ void ieee80211_tx_status_8023(struct ieee80211_hw *hw,
if (sta->status_stats.lost_packets)
sta->status_stats.lost_packets = 0;

- if (test_sta_flag(sta, WLAN_STA_TDLS_PEER_AUTH))
- sta->status_stats.last_tdls_pkt_time = jiffies;
+ sta->status_stats.last_pkt_time = jiffies;
} else {
ieee80211_lost_packet(sta, info);
}
--
2.25.1


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