Triggered by this blog post from Percona.
Problem could be reproduced with sysbench-tpcc and Percona settings. Buffer pool 25G for 100G data set (1000 warehouses). Datadir located on SSD. tpcc workload with 32 benchmark threads on hardware with 16 cores/32 hyperthreads.
Throughput starts high and then decreases over a varying time period (500 .. 1200 seconds) to reach ~200 tps. Performance schema shows lots of time spent with buf_pool_mutex. CPU usage of the mariadbd process is rather low around 300%.
MySQL 8.0 does not show that problem. MariaDB 10.5.4 performs better than pre-10.5.5 shapshot.