QDMA dma-perf: data is not received in user space when no_memcpy is enabled (ST C2H interface)

[ApoyanHovhannes]

Hello all,

dma-perf tool runs without errors, but no data is transferred to user space (with default configuration):

dma-perf -c dmaperf_config/st-c2h-pfetch1/st_1_1_pfetch-cmptsz1/c2h_st_1_1_pfetch-cmptsz1_4096

I found a place in the driver where data copying depends on the req->no_memcpy value, which is configured by dma-perf tool and enabled by default. When no_memcpy is disabled, the data is transferred to user space, but it also affects performance.

Is there a way to avoid intermediate copying and still receive data in user space? I want to understand whether the QDMA linux-kernel driver supports zero-copy or a similar mechanism.

[hmaarrfk]

That’s because the driver is fake news. And just keeps the data in the kernel memory since somebody needed a quick way to benchmark things.

[ApoyanHovhannes]

Thank you for the clarification.
I noticed your fork and your contribution to the linux-kernel QDMA driver.

I have a question about your fork. As far as I understand, the driver part mentioned in it remains unchanged, but I haven't had a chance to fully examine it yet. Have you changed this behavior in your fork to avoid intermediate copying and transferring data to user space?