Nexis

printf improving GPU performance???

Discussion created by Nexis on Jul 15, 2008
Latest reply on Aug 12, 2008 by Nexis

I accidentally discovered while testing my application that printing my kernel was improving the performance of my HD 3870...

I was also able to reproduce this behavior in the  simple_matmul example from the CAL SDK. If you run the sample with the default values, the output should be something like this:

Matrix Size     GPU Only        Total
(0256x0256)     65.5152         1.1904

If I put some printf at the start of the main() function, i get the following output:

Matrix Size     GPU Only        Total
(0256x0256)     151.7902        0.4275

Is anyone else able to reproduce this behavior?

To acheive this result you actually have to put quite a fiew printf... I print 100 times about 2000 characters:

for(int i=0; i<100; i++) printf("11111111111111111111.......11");

 You don't actually have to count 2000 character, just look at the column count in your editor to get 2000 "1"...

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