How to retrieve cpu usage per process

This article appears to provide the code you need to monitor CPU usage for a process using native Delphi. What follows is a direct quote from the above article.

Using the unit

When starting to monitor a process, call
cnt:=wsCreateUsageCounter(Process_id) to initialize a usage counter.
When you need to get the current CPU usage of that process, use
usage:=wsGetCpuUsage(cnt). When you have finished monitoring the
process, call wsDestroyUsageCounter(cnt) to free memory used by usage
counter and close open handles.

The uCpuUsage unit

unit uCpuUsage;

interface
const
    wsMinMeasurementInterval=250; {minimum amount of time that must have elapsed to calculate CPU usage, miliseconds. If time elapsed is less than this, previous result is returned, or zero, if there is no previous result.}
type
    TCPUUsageData=record
        PID,Handle:cardinal;
        oldUser,oldKernel:Int64;
        LastUpdateTime:cardinal;
        LastUsage:single;
        //Last result of wsGetCpuUsage is saved here
        Tag:cardinal;
        //Use it for anythin you like, not modified by this unit
    end;
    PCPUUsageData=^TCPUUsageData;

function wsCreateUsageCounter(PID:cardinal):PCPUUsageData;
function wsGetCpuUsage(aCounter:PCPUUsageData):single;
procedure wsDestroyUsageCounter(aCounter:PCPUUsageData);

implementation

uses Windows;

function wsCreateUsageCounter(PID:cardinal):PCPUUsageData;
var
    p:PCPUUsageData;
    mCreationTime,mExitTime,mKernelTime, mUserTime:_FILETIME;
    h:cardinal;
begin
    result:=nil;
    //We need a handle with PROCESS_QUERY_INFORMATION privileges
    h:=OpenProcess(PROCESS_QUERY_INFORMATION,false,PID);
    if h=0 then exit;
    new(p);
    p.PID:=PID;
    p.Handle:=h;
    p.LastUpdateTime:=GetTickCount;
    p.LastUsage:=0;
    if GetProcessTimes(p.Handle, mCreationTime, mExitTime, mKernelTime, mUserTime) then begin
        //convert _FILETIME to Int64
        p.oldKernel:=int64(mKernelTime.dwLowDateTime or (mKernelTime.dwHighDateTime shr 32));
        p.oldUser:=int64(mUserTime.dwLowDateTime or (mUserTime.dwHighDateTime shr 32));
        Result:=p;
    end else begin
        dispose(p);
    end;
end;

procedure wsDestroyUsageCounter(aCounter:PCPUUsageData);
begin
    CloseHandle(aCounter.Handle);
    dispose(aCounter);
end;

function wsGetCpuUsage(aCounter:PCPUUsageData):single;
var
    mCreationTime,mExitTime,mKernelTime, mUserTime:_FILETIME;
    DeltaMs,ThisTime:cardinal;
    mKernel,mUser,mDelta:int64;
begin
    result:=aCounter.LastUsage;
    ThisTime:=GetTickCount; //Get the time elapsed since last query

    DeltaMs:=ThisTime-aCounter.LastUpdateTime;
    if DeltaMs < wsMinMeasurementInterval then exit;
aCounter.LastUpdateTime:=ThisTime;

    GetProcessTimes(aCounter.Handle,mCreationTime, mExitTime, mKernelTime, mUserTime);
    //convert _FILETIME to Int64.
    mKernel:=int64(mKernelTime.dwLowDateTime or (mKernelTime.dwHighDateTime shr 32));
    mUser:=int64(mUserTime.dwLowDateTime or (mUserTime.dwHighDateTime shr 32));
    //get the delta
    mDelta:=mUser+mKernel-aCounter.oldUser-aCounter.oldKernel;

    aCounter.oldUser:=mUser;
    aCounter.oldKernel:=mKernel;

    Result:=(mDelta/DeltaMs)/100;
    //mDelta is in units of 100 nanoseconds, so…

    aCounter.LastUsage:=Result;
    //just in case you want to use it later, too
end;

end.