Trace-cmd, missing tracing_on

Hi,

I am seeing some crashes in iwlwifi, wanting to capture more info to debug it. So like outlined here,
https://wireless.wiki.kernel.org/en/users/drivers/iwlwifi/debugging

I'm trying to enable / run trace-cmd. I added it to my build, but when I try to execute it,

root@OpenWrt:/# trace-cmd record -e iwlwifi
trace-cmd: No such file or directory
  opening '/sys/kernel/debug/tracing/tracing_on'

Is this a known issue, or something I need to change to get the tracing working?

Thanks!