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tcige

fullscreen app, why cpu always 100% on old computer

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i do not use D3DPRESENT_INTERVAL_IMMEDIATE

 

although cpu is 100%, it's not stuck

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Could it be simply that your "old computer" has less CPU cycles to do the same work, so its load is 100% ? Its not all servicing your app, after all.

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Some drivers implement vsync kind of like this:

 

while (1)
{
    if (IsItTimeToVSyncYet ())
    {
        ActuallyDoThePresentCall ();
        break;
    }
}

 

That's going to chew 100% CPU even though it's not actually doing anything most of the time.

Edited by mhagain

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Could it be simply that your "old computer" has less CPU cycles to do the same work, so its load is 100% ? Its not all servicing your app, after all.

 

Or the driver overrides your VSync behavior. Both AMD & NVIDIA control panels allow this.

 

Some drivers implement vsync kind of like this:

 

while (1)
{
    if (IsItTimeToVSyncYet ())
    {
        ActuallyDoThePresentCall ();
        break;
    }
}

 

That's going to chew 100% CPU even though it's not actually doing anything most of the time.

 

i test that if cpu has only one core, it will always be 100% when fullscreen

 

i mean directx 9, and os is xp, maybe 5 to 10 years ago

 

i do not know if gpu good enough can help make cpu usage lower at that time

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