CPU Usage

Richard Andrew x64

Is there any way in Windows to throttle a process' CPU usage? If so, what's the technique? EDITED: I'm asking if one can programmatically throttle a process' CPU usage. Meaning managing the CPU time that a process is allowed to consume.

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Dave Kreskowiak

Not that I've ever seen. Thinking about it, you might be able to kind of simulate it by limiting the cores the process can run on by setting processor affinity for it.

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Lost User

Supposedly [JOBOBJECT_CPU_RATE_CONTROL_INFORMATION](https://learn.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-jobobject\_cpu\_rate\_control\_information) (passed into `SetInformationJobObject`) can be used for something like that. I've never used it, so I have no details beyond that.

Greg Utas

You can use these for your own process or another for which you have the required permission: SetPriorityClass function (processthreadsapi.h) - Win32 apps | Microsoft Learn[^] SetProcessAffinityMask function (winbase.h) - Win32 apps | Microsoft Learn[^] Apparently these can also be invoked via PowerShell or the Task Manager.

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Lost User

A tiny virtual machine.

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Lost User

Hi, If you mean you want to limit the process to a specific percentage (say 10% for example), then you can do this by attaching the process to a Job object. [Job Objects - Win32 apps | Microsoft Learn](https://learn.microsoft.com/en-us/windows/win32/procthread/job-objects) I think you would want JOB_OBJECT_CPU_RATE_CONTROL_ENABLE | JOB_OBJECT_CPU_RATE_CONTROL_HARD_CAP [JOBOBJECT_CPU_RATE_CONTROL_INFORMATION (winnt.h) - Win32 apps | Microsoft Learn](https://learn.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-jobobject\_cpu\_rate\_control\_information)

Richard Andrew x64

This looks awesome. Thanks, David.

The difficult we do right away... ...the impossible takes slightly longer.

Dave Kreskowiak

Nice. Learn something new every day. :thumbsup:

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Dave Kreskowiak

Dave Kreskowiak

I know this is the C/C++ forum, but here's an example of how to do this in C#. It was an interesting little research project. The result can be seen in Task Manager quite easily. The CPU is limited to an AVERAGE of 20% in this example. It'll go as low as 8% and as high as 25% on my 13900K.

using System.Diagnostics;
using System.Runtime.InteropServices;

namespace CsJobObjectSandbox
{
internal class Program
{
[StructLayout(LayoutKind.Explicit, Size = 8)]
public struct JobObject_CPU_Rate_Control_Information
{
[FieldOffset(0)]
public uint ControlFlags;

        \[FieldOffset(4)\]
        public uint CpuRate;
        \[FieldOffset(4)\]
        public uint Weight;

        \[FieldOffset(4)\]
        public ushort MinRate;
        \[FieldOffset(6)\]
        public ushort MaxRate;
    }

    \[StructLayout(LayoutKind.Sequential)\]
    public struct SECURITY\_ATTRIBUTES
    {
        public int nLength;
        public IntPtr lpSecurityDescriptor;
        public int bInheritHandle;
    }

    public enum JobObject\_Info\_Class
    {
        BasicLimitInformation = 2,
        BasicUiRestrictions = 4,
        SecurityLimitInformation = 5,
        EndOfJobItmeInformation = 6,
        AssociateCompletionPortInformation = 7,
        ExtendedLimitInformation = 9,
        GroupInformation = 11,
        NoticiationLimitInformation = 12,
        GroupInformationEx = 14,
        CpuRateControlInformation = 15,
        NetRateControlinformation = 32,
        NotificationLimitInformation = 33,
        LimitViolationInformation2 = 34
    }

    private const uint JOBOBJECT\_CPU\_RATE\_CONTROL\_ENABLE = 0x1;
    private const uint JOBOBJECT\_CPU\_RATE\_CONTROL\_WEIGHT\_BASED = 0x2;
    private const uint JOBOBJECT\_CPU\_RATE\_CONTROL\_HARD\_CAP = 0x4;
    private const uint JOBOBJECT\_CPU\_RATE\_CONTROL\_NOTIFY = 0x8;
    private const uint JOBOBJECT\_CPU\_RATE\_CONTROL\_MIN\_MAX\_RATE = 0x10;

    \[DllImport("kernel32.dll", CharSet = CharSet.Auto)\]
    static extern IntPtr CreateJobObject(\[In\] ref SECURITY\_ATTRIBUTES lpJobAttributes, string lpName);

    \[DllImport("kernel32.dll", CharSet = CharSet.Auto)\]
    static extern bool SetInformationJobObject(\[In\] IntPtr hJob, \[In\] JobObject\_Info\_Class jobObjectInfoClass, IntPtr lpJobObjectInfo, int cbJobObjectInfoLength);

    \[D

David Crow

Just out of curiosity, if you set a hard cap of 20%, what causes it to exceed that?

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Dave Kreskowiak

I don't know for sure, but I suspect thread scheduling on different cores running at different speeds. On a 13900, you have 8 performance cores, which support HT, and 16 efficiency cores, which don't support HT. So I have 24 cores that can run at vastly different speeds, supporting 32 threads.

Asking questions is a skill CodeProject Forum Guidelines Google: C# How to debug code Seriously, go read these articles.
Dave Kreskowiak