Support cpu limit in docker

[okhowang]

close #1824

on windows docker with process isolation, use job api to get cpu limit.
on linux docker, use cgroups to get cpu limit.

[jhasse]

Any idea why 1bcc689 did work for me?

[okhowang]

Any idea why 1bcc689 did work for me?

I notice that there are many arguments about cpu-limit.
https://docs.docker.com/config/containers/resource_constraints/
--cpus=<value> is using cgroup to limit cpu usage.
--cpuset-cpus is using cpu-affinity api to limit process run on specific cpus

so 1bcc689 work only when --cpuset-cpus is actived.
my patch work when --cpus is actived.

we should use minimal args when they both active.
for example
docker run --cpus 3 --cpuset-cpus 1,2,3,4 mean we have 3 core available.
docker run --cpus 3 --cpuset-cpus 1,2 mean we have 2 core available.

windows docker don't support --cpuset-cpus currently.

docker: Error response from daemon: invalid option: Windows does not support CpusetCpus.

[jhasse]

Thanks!

The detection code is quite long (especially the cgroups version). If we include this, we should definitely not run it, if the user specified a job count with -j.

[okhowang]

Thanks!

The detection code is quite long (especially the cgroups version). If we include this, we should definitely not run it, if the user specified a job count with -j.

I have modified ninja.cc to bypass GuessParallelism when -j set.

[jhasse]

Thanks and nice approach using the destructor to set it at the end of the scope :)

Looking forward to some further comments by others.

[rufinio]

Successfully tested --cpus=<value>

with following configuration:

• OS: Microsoft Windows Server 2022 Standard 10.0.20348
• Docker: version 20.10.7, build 40ef3b6
• Image: mcr.microsoft.com/dotnet/framework/sdk:4.8-windowsservercore-ltsc2022

[jhasse]

Anyone tested on Linux, especially start up time in different scenarios? (no idea how taxing those /proc opens can be)

[okhowang]

Anyone tested on Linux, especially start up time in different scenarios? (no idea how taxing those /proc opens can be)

I tested with time ninja --version(--version will read cpu limit config) on my WSL2 with version 1.10.0 and this MR.

my version

$ time ./ninja --version
1.10.2.git

real    0m0.023s
user    0m0.000s
sys     0m0.004s

system ninja

time ninja --version
1.10.0

real    0m0.002s
user    0m0.000s
sys     0m0.001s

[rufinio]

@jhasse: Anything else to get this PR merged?