On Thu, Nov 17, 2022, yosi yarchi wrote: > > 1. SAM9X35 (8 CAN mailboxes), > This is a *very* very low-end core (ARM926), so be careful that some latency issues would be expected. If you don't have a specific Linux use-case, maybe you can try something like ZephyrOS instead? Given that low-end core, and if you're stuck with Linux, a mainline kernel with preemption disabled (CONFIG_PREEMPT_NONE) might actually be more beneficial latency-wise than PREEMPT_RT... > 2. Linux mscb 5.4.41-linux4sam-2020.04-rt24 #1 PREEMPT_RT Wed Nov 9 > 06:12:28 UTC 2022 armv5tejl GNU/Linux "5.4.41-linux4sam-2020.04-rt24". This is a vendored RT kernel, and vendored RT kernels are known to have latency issues. Can you please try official RT kernels instead? More info is here: https://wiki.linuxfoundation.org/realtime/preempt_rt_versions Make sure that debugging options are disabled, e.g. CONFIG_PROVE_LOCKING, and so on. Afterwards, you'd like to measure the latencies of your (single-core) system with something like: cyclictest \ --default-system \ --secaligned \ --mlockall \ --interval=500 \ --priority=98 \ --histogram=2000 And then check the reported worst-case latencies. > 3. CAN threaded interrupt (irq/30-can0-346) is configured to be > highest priority on system. Please not that in RT, many system-critical kernel threads run at rtprio 99. The hight (sane) priority to be assigned should thus be 98. > > my problem is that from time to time I get CAN RX overflow. > That would be kinda expected with such a low-end core, even when everything else is "perfect". > > I've tried some solutions, no one worked out of the box: > > 1. disable all relevant irqs (timer, network) at CAN irq_handler > (irq_handler_entry: irq=30 name=can0), and enable them at the end of CAN > threaded interrupt job processing (at91_irq_r) > That's wrong in so many ways, please don't do that. > 2. configure CAN job (at91_irq) to run inside the CAN irq_handler > (irq_handler_entry: irq=30 name=can0) by adding IRQF_NO_THREAD flag to > request_irq. ditto. Good luck, -- Ahmed S. Darwish Linutronix GmbH
