Question

I’m currently writing an OpenCL kernel (but I suppose that in CUDA in will be the same), and currently I try to optimize for NVidia GPU.

I currently use 63 registers in my kernel, this kernel is very big and so it use all the GPU registers. I’m looking for some way to:

1) See which variables are in registers and which are then in global memory (Because if I have not enough registers it seems the compiler save the variables in global memory).

2) Is there a way to specify which variable is more important (or which should be in registers). Because I use some variables that are present but less used. A way to give priority ?

Is there other optimization strategy when we already use all the registers ?

BTW : I have also try to read the PTX code and search for all the “.reg” keywords but the problem is that the PTX is unreadable, I don’t know which register is used for which variable in my code. I have’nt find any way to have the correspondance !

thanks

Answer 1

See which variables are in registers and which are then in global
memory

For this i do not know the way how to check it, however

Is there a way to specify which variable is more important

One trick that i use when i see that i have spilled registers (due to lack of them or when i need to use dynamic indexing in local vars, which is bad) is to explicitly store ones, that i think are not so critical, into local memory (called “shared” in CUDA)

e.g. before:

uint16 somedata;

after:

__local uint16 somedata[WG_SIZE]; // or __local uint someadata[16];

but beware that if your local memory usage will be greatly increased you are risking to have penalty because number of inflight wavefronts will be less ( i.e. you might have lower occupancy)

Hope this helps.