NvBuffer mapping to GpuMat

Robotics & Edge Computing Jetson & Embedded Systems Jetson Nano
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1

I’m developing video streaming application, one important part is video processing.
I use Argus framework to capture video. All the frame processing is done in GPU, so, I want to minimize data transfers as much as possible.
I’m able to access NvBufer from CPU via NvBufferMemMap and NvBufferMemSyncForCpu, but it requires data transfer (convert cv::Mat to cv::cuda::GpuMat).
The second option is to create EGLImage via NvEGLImageFromFd, but as far as I understand this requires data copy from DMA buffer.

I also found NvBufferMemSyncForDevice, but I doesn’t work as I expect (it can’t be used to access data from GPU like it can be done from CPU via NvBufferMemSyncForCpu).

I also found this topic, but there was no direct solution to this problem.

As far as I know, Jetson Nano shares the same physical memory for CPU and GPU, so it seems like there is no fundamental limitation to directly map DMA buffer to GPU.

2

Hi,
Please refer to the patch:
LibArgus EGLStream to nvivafilter - #14 by DaneLLL

3

This patch still uses NvEGLImageFromFd. Is it true, that creation of EGLImage from NVBuffer implies a copy?

4

Hi,

No, it doesn’t copy the frame data. It is more like to wrap NvBuffer into EGLImage. To fill in data structure of EGLImage and frame data is in same memory.

5

Do I understand you correctly?

When I capture the frame - it lives in DMA buffer. NvBuffer is some kind of wrapper around DMA buffer. Then I create EGLImage from NVBuffer - still the same memory. Then pass EGLImage to GpuMat - it uses the same buffer.

So, pipeline Capture → NvBuffer → EGLImage → GpuMat doesn’t perform any copies of memory and everything is the same piece of memory. Is it right?

6

Hi,
Yes, it is correct.

7

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