Monitoring : Cpu usage stuck at 0% even if real cpu usage is at ~30%-40%

What's going wrong?

After updating to last pm2 version command pm2 ls display cpu at 0% usage but command pm2 monit display real cpu usage for ~30-40%

I use pm2-metrics which collect the 0% cpu from pm2 ls apparently.

How could we reproduce this issue?

Good question i dont know, for me it happened after updating pm2 to last version.

Supporting information

--- PM2 report ----------------------------------------------------------------
Date                 : Thu Sep 03 2020 15:10:43 GMT+0200 (UTC+02:00)
===============================================================================
--- Daemon -------------------------------------------------
pm2d version         : 4.4.1
node version         : 14.4.0
node path            : /home/ouraios/.npm-packages/bin/pm2
argv                 : /usr/bin/node,/home/ouraios/.npm-packages/lib64/node_modules/pm2/lib/Daemon.js
argv0                : node
user                 : ouraios
uid                  : 1001
gid                  : 100
uptime               : 12min
===============================================================================
--- CLI ----------------------------------------------------
local pm2            : 4.4.1
node version         : 14.4.0
node path            : /home/ouraios/.npm-packages/bin/pm2
argv                 : /usr/bin/node,/home/ouraios/.npm-packages/bin/pm2,report
argv0                : node
user                 : ouraios
uid                  : 1001
gid                  : 100
===============================================================================
--- System info --------------------------------------------
arch                 : x64
platform             : linux
type                 : Linux
cpus                 : Intel(R) Xeon(R) E-2136 CPU @ 3.30GHz
cpus nb              : 8
freemem              : 27916460032
totalmem             : 42949672960
home                 : /home/ouraios
===============================================================================
--- PM2 list -----------------------------------------------
┌─────┬────────────────┬─────────────┬─────────┬─────────┬──────────┬────────┬──────┬───────────┬──────────┬──────────┬──────────┬──────────┐
│ id  │ name           │ namespace   │ version │ mode    │ pid      │ uptime │ ↺    │ status    │ cpu      │ mem      │ user     │ watching │
├─────┼────────────────┼─────────────┼─────────┼─────────┼──────────┼────────┼──────┼───────────┼──────────┼──────────┼──────────┼──────────┤
│ 1   │ API_PROD       │ default     │ 0.0.0   │ cluster │ 19615    │ 59s    │ 1    │ online    │ 47%      │ 287.6mb  │ ouraios  │ disabled │
│ 4   │ API_PROD       │ default     │ 0.0.0   │ cluster │ 19650    │ 57s    │ 1    │ online    │ 59.8%    │ 377.3mb  │ ouraios  │ disabled │
└─────┴────────────────┴─────────────┴─────────┴─────────┴──────────┴────────┴──────┴───────────┴──────────┴──────────┴──────────┴──────────┘
Module
┌────┬───────────────────────────────────────┬────────────────────┬───────┬──────────┬──────┬──────────┬──────────┬──────────┐
│ id │ module                                │ version            │ pid   │ status   │ ↺    │ cpu      │ mem      │ user     │
├────┼───────────────────────────────────────┼────────────────────┼───────┼──────────┼──────┼──────────┼──────────┼──────────┤
│ 5  │ pm2-metrics                           │ 1.0.38             │ 16739 │ online   │ 0    │ 0%       │ 60.0mb   │ ouraios │
└────┴───────────────────────────────────────┴────────────────────┴───────┴──────────┴──────┴──────────┴──────────┴──────────┘
===============================================================================
--- Daemon logs --------------------------------------------
/home/ouraios/.pm2/pm2.log last 20 lines:
PM2        | 2020-09-03T14:57:55: PM2 log: App [API_PROD:1] starting in -cluster mode-
PM2        | 2020-09-03T14:57:55: PM2 log: App [API_PROD:1] onlinee-
PM2        | 2020-09-03T14:57:55: PM2 log: App [API_PROD:4] starting in -cluster mode-
PM2        | 2020-09-03T14:57:55: PM2 log: App [API_PROD:4] online
PM2        | 2020-09-03T14:57:55: PM2 log: App [pm2-metrics:5] starting in -fork mode-
PM2        | 2020-09-03T14:57:55: PM2 log: App [pm2-metrics:5] online
PM2        | 2020-09-03T15:09:44: PM2 log: App [API_PROD:1] starting in -cluster mode-
PM2        | 2020-09-03T15:09:44: PM2 log: App [API_PROD:1] online
PM2        | 2020-09-03T15:09:46: PM2 log: -reload- New worker listening
PM2        | 2020-09-03T15:09:46: PM2 log: Stopping app:API_PROD id:_old_1
PM2        | 2020-09-03T15:09:46: PM2 log: App name:API_PROD id:_old_1 disconnected
PM2        | 2020-09-03T15:09:46: PM2 log: App [API_PROD:_old_1] exited with code [0] via signal [SIGINT]
PM2        | 2020-09-03T15:09:46: PM2 log: pid=16610 msg=process killed
PM2        | 2020-09-03T15:09:46: PM2 log: App [API_PROD:4] starting in -cluster mode-
PM2        | 2020-09-03T15:09:46: PM2 log: App [API_PROD:4] online
PM2        | 2020-09-03T15:09:47: PM2 log: -reload- New worker listening
PM2        | 2020-09-03T15:09:47: PM2 log: Stopping app:API_PROD id:_old_4
PM2        | 2020-09-03T15:09:47: PM2 log: App name:API_PROD id:_old_4 disconnected
PM2        | 2020-09-03T15:09:47: PM2 log: App [API_PROD:_old_4] exited with code [0] via signal [SIGINT]
PM2        | 2020-09-03T15:09:48: PM2 log: pid=16643 msg=process killed

Start by comparing the CPU values shown by pm2 ls, pm2 monit, and the pm2-metrics exporter, using the supplied PM2 report and the update to version 4.4.1 as context. Trace how each command obtains CPU usage; done means the reported values agree with the real process usage and the regression has coverage, although no source file or test is named in the issue.