How does docker use CPU cores from its host operating system?

Question

My understading, based on the fact that Docker is based on LXC, is that Docker containers share various resources from its host operating system. My concern is with CPU cores. Here is a scenario:

• a host linux OS has 8 cores
• I have to deploy a set of docker containers on the host OS above.
• Some of the docker containers that I need to deploy would be better suited to use 2 cores

a) So if I run all of the docker containers on that host, will they consume CPU/cores as needed like if they were being run as normal installed applications on that host OS ?

b) Will the docker container consume its own process and all of the processing that is contained in it will be stuck to that parent process's CPU core ?

c) How can I specify a docker container to use a number of cores ( 4 for example ). I saw there is a -C flag that can point to a core id, but it appears there is no option to specify the container to pick N cores at random.

Answer 1

Currently, I don't think docker provides this level of granularity. It doesn't specify how many cores it allocates in its lxc.conf files, so you will get all cores for each docker, potentially (or possibly 1, I'm not 100% sure on that).

However, you could tweak the conf file generated for a given container and set something like

cpuset {     cpuset.cpus="0-3"; }