Raistmer

FCStacks influence on number of wavefronts in-flight

Discussion created by Raistmer on Sep 18, 2010
Latest reply on Sep 22, 2010 by himanshu.gautam
what values is too high?

"
FCStacks - The number of flow control stack size used by the kernel (only for GPU device). This number may affect the number of wavefronts in-flight. To reduce the stack size, reduce the amount of flow control nesting in the kernel.
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Could someone give some numbers, please. How this number will affect the number of simultaneously executed wavefronts on SIMD ?
For example one of my kernels has FCStacks ==2, another one FCStacks ==6.
In what case this number will be limiting factor?

EDIT: the kernel with FCStacks ==6 has pretty high GPR usage too, 55 GPRs used.
What will limit number of wavefronts in this case? GPR usage or FCStacks value?
And how many wavefronts per SIMD I could expect ?

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