docs: add hint howto get perf to show bpf JIT symbols

This section should be cleaned up, but just record this info here for now.

Thanks to Daniel Borkmann for teaching me this trick.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>

kernel/Documentation/bpf/troubleshooting.rst

@@ -135,3 +135,19 @@ The ``proglen`` is the len of opcode sequence generated and ``flen``
 is the number of bpf insns. You can use tools/net/bpf_jit_disasm.c to
 disassemble that output. bpf_jit_disasm -o will dump the related
 opcodes as well.
+
+Perf tool symbols
+=================
+
+For JITed progs, you can do sysctl net/core/bpf_jit_kallsyms=1
+and f.e. perf script --kallsyms=/proc/kallsyms to show them based
+on the tag::
+
+ sysctl net/core/bpf_jit_kallsyms=1
+
+Detail see commit: https://git.kernel.org/torvalds/c/74451e66d516c55e3
+
+Remember to use the perf command-line option --kallsyms=/proc/kallsyms
+to get the symobols resolved, like::
+
+ # perf report --no-children --kallsyms=/proc/kallsyms