cuFFT runtime changes current context

Accelerated Computing CUDA CUDA Programming and Performance
#1

I am building an application where I would like to create and manage my own CUDA contexts using the driver API. My understanding is that I should be able to create a context and have the CUDA runtime libraries use that context too. However, some particular cuFFT runtime calls appear to be changing the context, when I would like it to use the existing context. I have written a minimal example to demonstrate this:

#include <cuda.h>
#include <cufft.h>

#include <iostream>

int main()
{
cuInit(0);
CUcontext main_render_context;
// create main context
cuCtxCreate(&main_render_context, 0, 0);
// print
std::cout << "main ctx: " << main_render_context << std::endl;
// push
cuCtxPushCurrent(main_render_context);

// cufft
cufftHandle handle;
cufftCreate(&handle);
int fftDimensions[2] = { 2048, 2048 };
size_t fftSize;
cufftGetSizeMany(
handle,
2, fftDimensions,
NULL, 0, 0, // triple of embed, stride, distance (in)
NULL, 0, 0, // triple of embed, stride, distance (out)
CUFFT_C2C,
1,
&fftSize
);

CUcontext current_render_context;
cuCtxGetCurrent(&current_render_context);
// prints different to above
std::cout << "current ctx: " << current_render_context << std::endl;

}

Building and running the above with CUDA 11.1 results in different values being printed for the contexts. Is this the expected behaviour, and if so, how should I ensure that I can run commands in my chosen context after a call to cuFFT?

#2

I note that the call to:

cufftCreate(&handle);

doesn’t seem to be changing the context. Apart from this cufftGetSizeMany call, have you identified other cufft calls that change the context?

#3

I have not noted any other runtime calls which change the context other than this and the related cufftEstimateMany, but I have not gone digging any further. Other calls to cuFFT in my program (e.g. cufftExecC2C) do not appear to change the context.

#4

my guess is that the other context that is popping up here is the primary context.

Anyway you may wish to file a bug. As a workaround, I assume you know how to save and restore contexts - you can do that after your usage of these calls, if you wish.

#5

I have submitted a bug report with bug id 3209287.