1. Execute the perf command to check if it's installed; if not installed, then execute (on CentOS): sudo yum install perf
2. View hot functions in real-time: perf top --call-graph dwarf -p {PID}, check if you can see the function stack of mysqld. Issues such as AHI(Adaptive Hash Index) are relatively easy to identify.
3. Generate a flame graph.

# If mysqld is running inside a container,
# then copy the mysqld binary file to the same execution path on the host machine.
docker cp {ContainerId}

# Find the process number of mysqld.
ps -ef | grep mysqld

# Sample for 40 seconds.
perf record -F 99 -p {pid} -g --call-graph dwarf -- sleep 40

# Convert the binary perf.data to text form.
perf script > out.perf

# Generate a flame graph.
# For the download of the flame graph tool, see the end of the document.
./FlameGraph-master/stackcollapse-perf.pl out.perf > out.folded
./FlameGraph-master/flamegraph.pl out.folded > mysqld.svg

Flame graph tools: FlameGraph-master.zip