Hi Felix, Following is the background of the problem, how I traced to mutex_lock and why I propose rcu locks. Issue: On a 10Mbps upload / 50 Mbps download connection, the following issue reported. Video periodically freezes and/or appears delayed when on Zoom or Teams. 1. Video will freeze for 10 or 15 seconds periodically when on a call, but audio continues and the session doesn't drop. 2. The video still works but it appears delay (I move, but the video of my movement is noticeably delay by a second or so) Tracing to mutex_lock(sta_mutex): When I investigated, I found that the ucentral agent in openwifi fetches the station list periodically. Without the station list fetch, the video quality is just fine. I investigated the station list path and found this mutex_lock. I also see that earlier it was rcu_lock which protected the station list in this path. In this commit, https://github.com/torvalds/linux/commit/66572cfc30a4b764150c83ee5d842a3ce17991c9, rcu lock was changed to mutex lock without providing any reason. I also saw this comment just above the sta_mutex declaration. /* Station data */ /* * The mutex only protects the list, hash table and * counter, reads are done with RCU. */ struct mutex sta_mtx; So I reverted back the mutex_lock with rcu_lock and it just worked fine. We tested for more than 2 weeks before concluding this analysis. I think the usage of mutex_lock is impacting the tx / rx path somewhere and hence the issue. It is a challenge to trace the exact function though. Thanks & Regards Venkat On Wed, 21 Sept 2022 at 00:21, Felix Fietkau <nbd@xxxxxxxx> wrote: > > > On 20.09.22 20:27, Venkat Ch wrote: > > Hi Felix, > > > > Thank you. I browsed through the code. There seems to be sleep > > operations wcn36xx platform.ath11k does n't seem to have the sleep > > operations in sta_statistics. We are using ath11k based chipset. Will > > it impact things if we apply this patch for ath11k boards only as a > > platform specific patch? > I think it's a bad idea to keep this hack without understanding why it > helps at all. > > - Felix -- If you rest, you rust
