perf: Couldn't record kernel reference relocation symbol

What is your kernel? Is it from the linux distributive you use or is it compiled by you (how did you install it)?

First part of warning says about /proc/kallsyms - can you show output of the command (started from the same user you used to run perf)

ls -l  /proc/kallsyms
cat /proc/kallsyms | head

Second part of the perf message says about kptr_restrict sysctl setting. Can you do

cat /proc/sys/kernel/kptr_restrict

to check the setting. Basically, to profile the kernel symbols you should either disable kptr_restrict by setting it to zero (as described in https://lwn.net/Articles/420403/ or https://code.google.com/p/dart/wiki/Profiling):

# Run as root user - e.g. after doing "sudo bash"
echo 0 > /proc/sys/kernel/kptr_restrict

or (https://stackoverflow.com/a/20391360/196561)

sudo sh -c " echo 0 > /proc/sys/kernel/kptr_restrict"

or

echo 0 | sudo tee /proc/sys/kernel/kptr_restrict

or you can always run the perf from root user.

After setting kptr_restrict to zero or when running perf from root you should get no warning about kallsyms and will be able to profile kernel functions.

Update: seems that perf record always want access to kallsyms/restricted kptrs, even with userspace-only event (-e cycles:u)

This tutorial worked perfectly for me!

http://lost-and-found-narihiro.blogspot.com/2012/06/how-to-install-perf-kernel-performance.html

Copied from the tutorial:

$ cat /proc/sys/kernel/kptr_restrict
1
$ echo 0 > /proc/sys/kernel/kptr_restrict
$ cat /proc/sys/kernel/kptr_restrict
0