Reduce CPU usage

patrick22 · 07-05-2009, 01:14 PM

Hi,

i am deleting over 2000 files in a for loop, everything works ok except that the CPU usage is 100 % during this loop. Here is the Code:

Code:

for( size_t i = 0; i < filesO.GetCount(); i++ ) 
{
	DeleteFile( filesO.Item( i ) );
}

How can i prevent increased CPU usage? i have seen programs doing the same thing but the CPU usage remains under 20%.

Is it there a way to do that without using sleep functions?

Thanks in advance.

legit · 07-05-2009, 01:38 PM

Get a new CPU.

patrick22 · 07-05-2009, 01:56 PM

Do you mean it is only possible with sleep functions?!

scwizzo · 07-05-2009, 08:21 PM

Loops eat CPU power period. The power consumed is somewhat based off what is inside the loop. Take the following code for example. It pegs out my CPU at 50% (100% on one of two cores).

Code:

#include <iostream> 
#include <string>
using namespace std;

int main()
{
    int temp = 999999999;
    for(int i = 0; i < temp; i++);
    return 0;	
}

Then take the other piece of code for example. This does 20% of one core.

Code:

#include <iostream> 
#include <string>
#include <conio.h>
using namespace std;

int main()
{    
    while(!_kbhit());
    return 0;	
}

Hopefully this gives you some insight in to reducing the CPU usage, however, Sleep() may be your only choice. How long does it take to delete 2000+ files?

patrick22 · 07-05-2009, 08:28 PM

Quote:

How long does it take to delete 2000+ files?

it takes less than 6 secondes.

Cactus_Hugger · 07-05-2009, 08:59 PM

Quote:

Originally Posted by patrick22

it takes less than 6 secondes.

Why is this a problem? You're asking the computer to do something, but you dislike the fact that it is doing it. You're deleting 2000 files -- I would have expected such an operation to be bottlenecked by disk IO, but perhaps it is getting buffered somewhere.

Certainly you could reduce CPU usage by inserting calls to Sleep(), but then the operation would take longer to complete. Just do what you need to do, as fast as you can. Reduce CPU with better algorithms or not spinning your wheels waiting for something to happen (neither of which seem possible here). Asking the computer to do something and asking it to not use CPU power are mutually exclusive. Reduce the amount of work you have to do in the first place, and you'll reap the resource gains there.

**Salem** · 07-05-2009, 10:23 PM

> i have seen programs doing the same thing but the CPU usage remains under 20%.
Do they also take 6 seconds?

Elysia · 07-06-2009, 05:50 AM

You can make a program that deletes the files in 6 seconds with 100% cpu use...
Or you can make a program that takes 30 seconds with 20% cpu use...
Your choice.
You can't have one and the other.

brewbuck · 07-08-2009, 09:39 PM

Quote:

Originally Posted by Elysia

You can make a program that deletes the files in 6 seconds with 100% cpu use...
Or you can make a program that takes 30 seconds with 20% cpu use...
Your choice.
You can't have one and the other.

Deleting files is an entirely I/O bound operation. It should NEVER consume 100% of the CPU. Something is wrong somewhere.

iMalc · 07-10-2009, 02:13 PM

Quote:

Originally Posted by brewbuck

Deleting files is an entirely I/O bound operation. It should NEVER consume 100% of the CPU. Something is wrong somewhere.

Yeah that's what I would think too.
Or perhaps some kind of "Software RAID" is in use?

07-05-2009, 01:14 PM	#1
patrick22 Registered User Join Date: Jan 2008 Posts: 42	Reduce CPU usage Hi, i am deleting over 2000 files in a for loop, everything works ok except that the CPU usage is 100 % during this loop. Here is the Code: Code: for( size_t i = 0; i < filesO.GetCount(); i++ ) { DeleteFile( filesO.Item( i ) ); } How can i prevent increased CPU usage? i have seen programs doing the same thing but the CPU usage remains under 20%. Is it there a way to do that without using sleep functions? Thanks in advance.
patrick22 is offline

07-05-2009, 01:38 PM	#2
legit Student Join Date: Aug 2008 Location: UK -> Newcastle Posts: 156	Get a new CPU. __________________ MSDN <- Programmers Haven!
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07-05-2009, 01:56 PM	#3
patrick22 Registered User Join Date: Jan 2008 Posts: 42	Do you mean it is only possible with sleep functions?!
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07-05-2009, 08:21 PM	#4
scwizzo Registered User Join Date: Mar 2007 Posts: 333	Loops eat CPU power period. The power consumed is somewhat based off what is inside the loop. Take the following code for example. It pegs out my CPU at 50% (100% on one of two cores). Code: #include <iostream> #include <string> using namespace std; int main() { int temp = 999999999; for(int i = 0; i < temp; i++); return 0; } Then take the other piece of code for example. This does 20% of one core. Code: #include <iostream> #include <string> #include <conio.h> using namespace std; int main() { while(!_kbhit()); return 0; } Hopefully this gives you some insight in to reducing the CPU usage, however, Sleep() may be your only choice. How long does it take to delete 2000+ files? __________________ home page (new layout)
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07-05-2009, 10:23 PM	#7
Salem and the hat of vanishing Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,214	> i have seen programs doing the same thing but the CPU usage remains under 20%. Do they also take 6 seconds? __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut. Up to 8Mb PlusNet broadband from only £5.99 a month!
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