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If i understood correctly, the kms driver (vc4-kms-v3d) uses a dynamic memory split which can be set via the 'cma' parameter in cmdline.txt

This means the less memory i assign to the gpu with 'gpu_mem' the more memory will be available for the dynamic gpu/cpu memory split.

When 'gpu_mem' is set to 16, the gpu will be initialized in a cutdown mode. Meaning some blocks are not active. I could see for example that gstreamer was missing some hardware decoder elements in this case.

But what are the further impacts? I can run chromium quiet smoothly and also playback a mjpeg video stream using gstreamer (1024 * 688) with no recognizable impact.

Is the 'gpu_mem=16' setting ok to use in combination with the kms driver? Or should i rather use 32M to initialize the gpu completely?

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  • Are you sure getting 16 MB of RAM free is worth the effort? Mar 2, 2021 at 7:05
  • @DmitryGrigoryev probably not. But I still want to know exactly whats going on. Or tbh I also wanted to know if i was completely off and there is something i misunderstood.
    – Fl0v0
    Mar 2, 2021 at 10:17

1 Answer 1

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In mesa3d's VC4 documentation's 'Performance Tricks' section, it is hinted that ;

  • Decrease firmware memory

The firmware allocates a fixed chunk of memory before booting Linux. If firmware functions are not required, this amount can be reduced.

In config.txt edit gpu_mem to 16, if you do not need video decoding, edit gpu_mem to 64 if you need video decoding.

One could infer that setting gpu_mem to 16 (or to less than 64, which it is is not clear) at least disables hardware video decoding.

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