CPU resources during docker build command on Windows

How can one control how many logical processors are used by docker build command on Windows?

I have this dockerfile:

FROM mcr.microsoft.com/windows/servercore:1803
SHELL ["powershell", "-NoLogo"]
RUN Get-ComputerInfo -Property *proc*
CMD Get-ComputerInfo -Property *proc*

and when I build an image I see the following output:

CsNumberOfLogicalProcessors : 2
CsNumberOfProcessors        : 1

Note that my computer has 4 logical processors and when I run container with --cpus 4 option I get an expected result:

CsNumberOfLogicalProcessors : 4
CsNumberOfProcessors        : 1

What confuses me is why docker build does not support --cpus option since it runs containers when creating image layers.

Docker info:

Containers: 0
 Running: 0
 Paused: 0
 Stopped: 0
Images: 41
Server Version: 18.09.0
Storage Driver: windowsfilter
 Windows:
Logging Driver: json-file
Plugins:
 Volume: local
 Network: ics l2bridge l2tunnel nat null overlay transparent
 Log: awslogs etwlogs fluentd gelf json-file local logentries splunk syslog
Swarm: inactive
Default Isolation: hyperv
Kernel Version: 10.0 17763 (17763.1.amd64fre.rs5_release.180914-1434)
Operating System: Windows 10 Pro Version 1809 (OS Build 17763.194)
OSType: windows
Architecture: x86_64
CPUs: 4
Total Memory: 7.891GiB
Name: Robo
ID: K3BP:UY7Z:JEXA:EJZ6:IYK6:WMW4:L4P4:5GTY:VR7K:SQKR:5QMO:AIEA
Docker Root Dir: C:\ProgramData\Docker
Debug Mode (client): false
Debug Mode (server): true
 File Descriptors: -1
 Goroutines: 28
 System Time: 2018-12-16T16:48:59.7060639Z
 EventsListeners: 1
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false
Product License: Community Engine

Solution

Not supported currently. You can track issue here https://github.com/moby/moby/issues/38387