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AM3517 excessive processing of NET_RX software interrupts

Reinyn Bedlington
Intellectual 380 points
Other Parts Discussed in Thread: AM3517

We are using the AM3517 (3.00.01.06 PSP, 2.6.32 kernel)

We have a USB connection to the Host PC and are using the Gadget / RNDIS for Ethernet over USB and we also have CAN traffic coming into the 3517.

Our application needs fairly low latency and occasionally the application will hang for > 100ms.

Debugging has indicated that NET_RX software interrupts are being processed while the app is hung. This can occasionally last nearly a full second.

This behavior is very sporadic and may only happen a few times per hour.

Any advice on debugging this would be helpful. I already tried compiling a preempting kernel and running our process with maximum priority, but there was no change in behavior.

Thnak you,

-Reinyn

  • 0
    Intellectual 380 points

    After further testing it looks like the CAN driver is the cause. I'm still not sure what exactly is causing the CAN driver to spend excessive time in NET_RX, but disabling the CAN interface (ifconfig can0 down) stops the application timeouts from happening.

    Of course we still need the CAN interface so any ideas would be appreciated.

  • 0 in reply to Reinyn Bedlington
    Intellectual 380 points

    I have narrowed the stalling of the CAN port down to this method call

    ti_hecc_rx_poll in (linux-2.6.32-psp03.00.01.06.sdk/drivers/net/can/ti_hecc.c)

    I have seen this call take over 200ms. I have also seen this method called multiple times in a row for 7ms per call. Which stalls out application.

    Are there any CAN \ Driver experts around?

    thanks,

    -Reinyn