problem with cpu utilizationand phpfpm_process_last_request_cpu

[freedomwarrior]

I'm trying to understand how the metric phpfpm_process_last_request_cpu works.

I created a simple docker-compose app with nginx, php-fpm and simple php stress test script.
Also, I monitor docker with cadvisor.
When I run a stress test, I see that a single php-fpm process utilizes 100% of the container CPU and I can see this on a graph of the cadvisor exporter.
But metric phpfpm_process_last_request_cpu did not show this utilisation, I always see 0 value with short spikes.
At this screenshot, top graph is phpfpm_process_last_request_cpu and bottom graph is cadvisor cpu usage of container.

So, does phpfpm_process_last_request_cpu must reflect real CPU usage or I just misunderstood this metric?
Thank you.