There are multiple limits. All must be satisfied.
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The maximum number of threads in the block is limited to 1024. This is the product of whatever your threadblock dimensions are (xyz). For example (32,32,1) creates a block of 1024 threads. (33,32,1) is not legal, since
33*32*1> 1024. -
The maximum x-dimension is 1024. (1024,1,1) is legal. (1025,1,1) is not legal.
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The maximum y-dimension is 1024. (1,1024,1) is legal. (1,1025,1) is not legal.
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The maximum z-dimension is 64. (1,1,64) is legal. (2,2,64) is also legal. (1,1,65) is not legal.
Also, threadblock dimensions of 0 in any position are not legal.
Your choice of threadblock dimensions (x,y,z) must satisfy each of the rules 1-4 above.
You should also do proper cuda error checking. Not sure what that is? Google “proper cuda error checking” and take the first hit.
Also run your codes with cuda-memcheck.
Do these steps before asking others for help. Even if you don’t understand the error output, it will be useful to others trying to help you.