docker-compose spec says cpus option is deprecated but docker run says use --cpus

Question

Reading docker-compose spec (https://github.com/compose-spec/compose-spec/blob/master/spec.md#cpus) it says that cpus option is DEPRECATED, so even if it still works when I use it, I think it is not a great idea.

cpus

DEPRECATED: use deploy.reservations.cpus

cpus define the number of (potentially virtual) CPUs to allocate to service containers. This is a fractional number. 0.000 means no limit.

On the other hand, docker run docs says (https://docs.docker.com/config/containers/resource_constraints/#configure-the-default-cfs-scheduler) that --cpus option is more convenient.

Specify the CPU CFS scheduler period, which is used alongside --cpu-quota. Defaults to 100000 microseconds (100 milliseconds). Most users do not change this from the default. For most use-cases, --cpus is a more convenient alternative.

So I'm very confused: should or shouldn't i use cpus in docker-compose? if don't, how do I efficiently control a service cpu usage?

I'm using docker without swarm.

Context

$ docker version
Client:
 Version:           20.10.2
 API version:       1.41
 Go version:        go1.13.8
 Git commit:        20.10.2-0ubuntu1~20.04.2
 Built:             Tue Mar 30 21:24:57 2021
 OS/Arch:           linux/amd64
 Context:           default
 Experimental:      true

Server:
 Engine:
  Version:          20.10.2
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.13.8
  Git commit:       20.10.2-0ubuntu1~20.04.2
  Built:            Mon Mar 29 19:10:09 2021
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.3.3-0ubuntu2.3
  GitCommit:        
 runc:
  Version:          spec: 1.0.2-dev
  GitCommit:        
 docker-init:
  Version:          0.19.0
  GitCommit:        

$ docker-compose version
docker-compose version 1.29.2, build 5becea4c
docker-py version: 5.0.0
CPython version: 3.7.10
OpenSSL version: OpenSSL 1.1.0l  10 Sep 2019

Answer 1

you should use deploy.reservations.cpus as the warning suggests, example: https://github.com/compose-spec/compose-spec/blob/master/deploy.md#cpus

services:
  frontend:
    image: awesome/webapp
    deploy:
      resources:
        limits:
          cpus: '0.50'
          memory: 50M
        reservations:
          cpus: '0.25'
          memory: 20M

so what it means is cpus should be under reservations, under deploy.