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* [PATCH v2] wifi: mac80211: Fix performance issue with mutex_lock
@ 2022-09-15  4:35 venkatch
  2022-09-20  7:24 ` [wifi] 662cceb50e: BUG:sleeping_function_called_from_invalid_context_at_include/linux/sched/mm.h kernel test robot
  2022-09-20  8:33 ` [PATCH v2] wifi: mac80211: Fix performance issue with mutex_lock Felix Fietkau
  0 siblings, 2 replies; 10+ messages in thread
From: venkatch @ 2022-09-15  4:35 UTC (permalink / raw)
  To: johannes; +Cc: linux-wireless, Venkat Chimata

From: Venkat Chimata <venkata@shasta.cloud>

OpenWiFi's ucentral agent periodically (typically 120 seconds)
issues nl80211 call to get associated client list from the
WLAN driver. Somehow this operation was causing tx/rx delays
sometimes and the video calls on connected clients are experiencing
jitter. The associated client list was protected by
a mutex lock. I saw that ieee80211_check_fast_xmit_all uses
rcu_read_lock and rcu_read_unlock to iterate through sta_list.
I took it as a refernce and changed the lock to rcu_read lock
from mutex.
Also saw this this comment just above sta_mutex declaration.
        /* Station data */
        /*
         * The mutex only protects the list, hash table and
         * counter, reads are done with RCU.
         */
        struct mutex sta_mtx;

Hence tried changing mutex_lock(/unlock) in ieee80211_dump_station
to rcu_read_lock(/unlock) and it resolved the jitter issue in the
video calls.

Tests:
We had this issue show up consistently and the patch fixed the issue.
We spent a good part of 2 weeks following up on this and with this
fix, the video calls are smooth.

Also tested if this could cause any crashes with below mentioned
process.

1. Connect 3 clients
2. A script running dumping clients in an infinite loop
3. Continuously disconnect / connect one client to see if
   there is any crash. No crash was observed.

---
v2:
* Resolve warning
 net/mac80211/cfg.c:858:33: warning:
 unused variable 'local' [-Wunused-variable]
 ---

Signed-off-by: Venkat Chimata <venkata@shasta.cloud>
---
 net/mac80211/cfg.c      | 7 ++-----
 net/mac80211/sta_info.c | 3 +--
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index 6a8350d..a005364 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -790,20 +790,17 @@ static int ieee80211_dump_station(struct wiphy *wiphy, struct net_device *dev,
 				  int idx, u8 *mac, struct station_info *sinfo)
 {
 	struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
-	struct ieee80211_local *local = sdata->local;
 	struct sta_info *sta;
 	int ret = -ENOENT;
 
-	mutex_lock(&local->sta_mtx);
-
+	rcu_read_lock();
 	sta = sta_info_get_by_idx(sdata, idx);
 	if (sta) {
 		ret = 0;
 		memcpy(mac, sta->sta.addr, ETH_ALEN);
 		sta_set_sinfo(sta, sinfo, true);
 	}
-
-	mutex_unlock(&local->sta_mtx);
+	rcu_read_unlock();
 
 	return ret;
 }
diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index 550a610..af6fa75 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -231,8 +231,7 @@ struct sta_info *sta_info_get_by_idx(struct ieee80211_sub_if_data *sdata,
 	struct sta_info *sta;
 	int i = 0;
 
-	list_for_each_entry_rcu(sta, &local->sta_list, list,
-				lockdep_is_held(&local->sta_mtx)) {
+	list_for_each_entry_rcu(sta, &local->sta_list, list) {
 		if (sdata != sta->sdata)
 			continue;
 		if (i < idx) {
-- 
2.34.1


^ permalink raw reply related	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2022-09-21 10:38 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2022-09-15  4:35 [PATCH v2] wifi: mac80211: Fix performance issue with mutex_lock venkatch
2022-09-20  7:24 ` [wifi] 662cceb50e: BUG:sleeping_function_called_from_invalid_context_at_include/linux/sched/mm.h kernel test robot
2022-09-20  8:33 ` [PATCH v2] wifi: mac80211: Fix performance issue with mutex_lock Felix Fietkau
     [not found]   ` <CABHL29H75U-0dBP14d-6ds-xMPt1eqrvQPuMp3oY8qQS8Y3Dbw@mail.gmail.com>
2022-09-20  9:10     ` Felix Fietkau
2022-09-20 18:27       ` Venkat Ch
2022-09-20 18:51         ` Felix Fietkau
2022-09-20 19:23           ` Venkat Ch
2022-09-21  8:05             ` Felix Fietkau
2022-09-21  8:31               ` Venkat Ch
2022-09-21 10:38                 ` Felix Fietkau

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