CPU and RAM percentage of usage metrics

從 README 中的 ProcessCollector 文件以及 issue 中顯示的 process_* 指標開始。釐清專案是否應新增 CPU 和 RAM 百分比指標、GPU 支援是否在範圍內，以及應如何定義測量方式；issue 未列出檔案、測試或完成標準。

I need to collect the percentage of usage of CPU and RAM.

I've seen from the README that for Linux these metrics are available with the class ProcessCollector. Indeed I see something just starting the server with start_http_server(8000).

Then, by connecting to localhost:8000, I see an output like this:

# HELP python_gc_objects_collected_total Objects collected during gc
# TYPE python_gc_objects_collected_total counter
python_gc_objects_collected_total{generation="0"} 618.0
python_gc_objects_collected_total{generation="1"} 620.0
python_gc_objects_collected_total{generation="2"} 0.0
# HELP python_gc_objects_uncollectable_total Uncollectable object found during GC
# TYPE python_gc_objects_uncollectable_total counter
python_gc_objects_uncollectable_total{generation="0"} 0.0
python_gc_objects_uncollectable_total{generation="1"} 0.0
python_gc_objects_uncollectable_total{generation="2"} 0.0
# HELP python_gc_collections_total Number of times this generation was collected
# TYPE python_gc_collections_total counter
python_gc_collections_total{generation="0"} 329.0
python_gc_collections_total{generation="1"} 29.0
python_gc_collections_total{generation="2"} 2.0
# HELP python_info Python platform information
# TYPE python_info gauge
python_info{implementation="CPython",major="3",minor="7",patchlevel="4",version="3.7.4"} 1.0
# HELP process_virtual_memory_bytes Virtual memory size in bytes.
# TYPE process_virtual_memory_bytes gauge
process_virtual_memory_bytes 2.096193536e+09
# HELP process_resident_memory_bytes Resident memory size in bytes.
# TYPE process_resident_memory_bytes gauge
process_resident_memory_bytes 2.752512e+08
# HELP process_start_time_seconds Start time of the process since unix epoch in seconds.
# TYPE process_start_time_seconds gauge
process_start_time_seconds 1.6355184461e+09
# HELP process_cpu_seconds_total Total user and system CPU time spent in seconds.
# TYPE process_cpu_seconds_total counter
process_cpu_seconds_total 3.6799999999999997
# HELP process_open_fds Number of open file descriptors.
# TYPE process_open_fds gauge
process_open_fds 7.0
# HELP process_max_fds Maximum number of open file descriptors.
# TYPE process_max_fds gauge
process_max_fds 1.048576e+06

How can I customize this output in order to have RAM, CPU (and eventually GPU) percentage of usage?

For example, I see process_cpu_seconds_total 3.6799999999999997 but I'd like to have something like process_cpu_perc_total 50%. The same for the RAM.