Correct code to get CPU usage [Win32 API]

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From: nki00 on 4 Jun 2010 19:06

Hi everyone:

I've been struggling to come up with a correct code to determine CPU usage
on the Windows-based system. So far I came up with the following. The code
is called internally from WM_TIMER message that is called once every 100
milliseconds, but if compared with the Task Manager's CPU usage, it does not
always match. What could be the reason for that?

int g_nCPU_usage_percent; //Global variable
.....

SetTimer(m_hMainWndHandle, TIMER_ID, 100, NULL);

.....

void OnTimer(UINT nIDEvent)
{
g_nCPU_usage_percent = GetCPU_Usage();
}

.....

int GetCPU_Usage()
{
//RETURN:
// = Percentage value [0-100], or
// = -1 if not known, or error

int nRes = -1;
FILETIME ftIdle, ftKrnl, ftUsr;
if(GetSystemTimes(&ftIdle, &ftKrnl, &ftUsr))
{
static BOOL bUsedOnce = FALSE;
static ULONGLONG uOldIdle = 0;
static ULONGLONG uOldKrnl = 0;
static ULONGLONG uOldUsr = 0;

ULONGLONG uIdle = ((ULONGLONG)ftIdle.dwHighDateTime << 32) |
ftIdle.dwLowDateTime;
ULONGLONG uKrnl = ((ULONGLONG)ftKrnl.dwHighDateTime << 32) |
ftKrnl.dwLowDateTime;
ULONGLONG uUsr = ((ULONGLONG)ftUsr.dwHighDateTime << 32) |
ftUsr.dwLowDateTime;

//Only if we have previous values
if(bUsedOnce)
{
ULONGLONG uDiffIdle = uIdle - uOldIdle;
ULONGLONG uDiffKrnl = uKrnl - uOldKrnl;
ULONGLONG uDiffUsr = uUsr - uOldUsr;

if(uDiffKrnl + uDiffUsr)
{
//Calculate percentage
nRes = (int)((uDiffKrnl + uDiffUsr - uDiffIdle) * 100 / (uDiffKrnl +
uDiffUsr));
}
}

//Remember data
bUsedOnce = TRUE;
uOldIdle = uIdle;
uOldKrnl = uKrnl;
uOldUsr = uUsr;
}

return nRes;
}

From: Jackie on 5 Jun 2010 05:43

nki00 wrote:
> Hi everyone:
>
>
> I've been struggling to come up with a correct code to determine CPU usage
> on the Windows-based system. So far I came up with the following. The code
> is called internally from WM_TIMER message that is called once every 100
> milliseconds, but if compared with the Task Manager's CPU usage, it does not
> always match. What could be the reason for that?
>
>
> int g_nCPU_usage_percent; //Global variable
> ....
>
> SetTimer(m_hMainWndHandle, TIMER_ID, 100, NULL);
>
> ....
>
> void OnTimer(UINT nIDEvent)
> {
> g_nCPU_usage_percent = GetCPU_Usage();
> }
>
>
> ....
>
>
> int GetCPU_Usage()
> {
> //RETURN:
> // = Percentage value [0-100], or
> // = -1 if not known, or error
>
> int nRes = -1;
> FILETIME ftIdle, ftKrnl, ftUsr;
> if(GetSystemTimes(&ftIdle,&ftKrnl,&ftUsr))
> {
> static BOOL bUsedOnce = FALSE;
> static ULONGLONG uOldIdle = 0;
> static ULONGLONG uOldKrnl = 0;
> static ULONGLONG uOldUsr = 0;
>
> ULONGLONG uIdle = ((ULONGLONG)ftIdle.dwHighDateTime<< 32) |
> ftIdle.dwLowDateTime;
> ULONGLONG uKrnl = ((ULONGLONG)ftKrnl.dwHighDateTime<< 32) |
> ftKrnl.dwLowDateTime;
> ULONGLONG uUsr = ((ULONGLONG)ftUsr.dwHighDateTime<< 32) |
> ftUsr.dwLowDateTime;
>
> //Only if we have previous values
> if(bUsedOnce)
> {
> ULONGLONG uDiffIdle = uIdle - uOldIdle;
> ULONGLONG uDiffKrnl = uKrnl - uOldKrnl;
> ULONGLONG uDiffUsr = uUsr - uOldUsr;
>
> if(uDiffKrnl + uDiffUsr)
> {
> //Calculate percentage
> nRes = (int)((uDiffKrnl + uDiffUsr - uDiffIdle) * 100 / (uDiffKrnl +
> uDiffUsr));
> }
> }
>
> //Remember data
> bUsedOnce = TRUE;
> uOldIdle = uIdle;
> uOldKrnl = uKrnl;
> uOldUsr = uUsr;
> }
>
> return nRes;
> }
>
>

I remember working on a process manager sime time ago in C#. It seems
like I used WMI and PercentProcessorTime from
Win32_PerfFormattedData_PerfOS_Processor to get processes' usage or
something like that. Maybe you can try to look at that?

--
Regards,
Jackie

From: Jackie on 5 Jun 2010 06:31

From: Bob Masta on 5 Jun 2010 08:14

On Fri, 4 Jun 2010 16:06:43 -0700, "nki00"
<lukkycharm1(a)gmail.com> wrote:

>Hi everyone:
>
>
>I've been struggling to come up with a correct code to determine CPU usage
>on the Windows-based system. So far I came up with the following. The code
>is called internally from WM_TIMER message that is called once every 100
>milliseconds, but if compared with the Task Manager's CPU usage, it does not
>always match. What could be the reason for that?
>
>
>int g_nCPU_usage_percent; //Global variable
>....
>
>SetTimer(m_hMainWndHandle, TIMER_ID, 100, NULL);
>
>....
>
>void OnTimer(UINT nIDEvent)
>{
> g_nCPU_usage_percent = GetCPU_Usage();
>}
>
>
>....
>
>
>int GetCPU_Usage()
>{
> //RETURN:
> // = Percentage value [0-100], or
> // = -1 if not known, or error
>
> int nRes = -1;
> FILETIME ftIdle, ftKrnl, ftUsr;
> if(GetSystemTimes(&ftIdle, &ftKrnl, &ftUsr))
> {
> static BOOL bUsedOnce = FALSE;
> static ULONGLONG uOldIdle = 0;
> static ULONGLONG uOldKrnl = 0;
> static ULONGLONG uOldUsr = 0;
>
> ULONGLONG uIdle = ((ULONGLONG)ftIdle.dwHighDateTime << 32) |
>ftIdle.dwLowDateTime;
> ULONGLONG uKrnl = ((ULONGLONG)ftKrnl.dwHighDateTime << 32) |
>ftKrnl.dwLowDateTime;
> ULONGLONG uUsr = ((ULONGLONG)ftUsr.dwHighDateTime << 32) |
>ftUsr.dwLowDateTime;
>
> //Only if we have previous values
> if(bUsedOnce)
> {
> ULONGLONG uDiffIdle = uIdle - uOldIdle;
> ULONGLONG uDiffKrnl = uKrnl - uOldKrnl;
> ULONGLONG uDiffUsr = uUsr - uOldUsr;
>
> if(uDiffKrnl + uDiffUsr)
> {
> //Calculate percentage
> nRes = (int)((uDiffKrnl + uDiffUsr - uDiffIdle) * 100 / (uDiffKrnl +
>uDiffUsr));
> }
> }
>
> //Remember data
> bUsedOnce = TRUE;
> uOldIdle = uIdle;
> uOldKrnl = uKrnl;
> uOldUsr = uUsr;
> }
>
> return nRes;
>}

This approach is used by "ejor" at
<http://www.codeproject.com/KB/threads/Get_CPU_Usage.aspx>

But he warns that it doesn't give the correct
results with a multiprocessor system. I didn't
download his complete code, but he says it has a
solution for that.

Best regards,

Bob Masta

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From: alain on 5 Jun 2010 09:32

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