Strange behaviour of mailbox calls - Raspberry Pi Forums

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i have user defined code want execute on videocore iv gpu. can execute code either via mailbox-call or via register-poking, writing directly v3d registers (see functions gpu_fft_base_exec_direct , gpu_fft_base_exec of https://github.com/raspberrypi/userland ... fft_base.c). additionally, i'm executing code several successive times on qpus.

now, executing code via directly poking registers (in loop: writing v3d registers, waiting interrupts) works perfectly. executing same code via mailbox interface shows strange behavior:
  • if there delay (e.g. 10 ms) between mailbox-calls, execution finishes successfully.
  • if there no delay between mailbox-calls, after few loop-iterations, system freezes, no response, not in terminals.
  • if set delay between syscalls lower value (e.g. 100 us), execution finished, (about 1/8th) slower!

theory first 2 points is, somehow swamp linux kernel syscalls, has no more time else!? can't explain why lower delay results in slower execution.

has here explanation behaviour?



raspberrypi



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