Re: CPU load inhibits CAN interrupts

[Wolfgang Grandegger <wg@grandegger.com>]

On 04/10/2012 04:40 PM, Krzysztof Witkowski wrote:
> I have an Ubuntu box with 3.2 kernel, CPU with 2 cores and PEAK-PCI card
> (SJA1000 controller attached via PCI bus)
> 
> I'm testing receive capabilities of the card on 1Mbit network using
> peak_pci module. It can handle about ~4000 packets per second, the
> corresponding interrupt is also raised ~4000 times per second (as
> /proc/interrupts shows) and it does not cause high CPU load on the system.
> 
> However, if I generate artificial CPU load with stress command:
> 
>    chrt --idle 0 stress -c 2

What does "-c 2" do? My "chrt" command does not have that option.

> the Receive Interrupts from SJA1000 are no longer raised at all and
> therefore no messages are received. At the same time network card (e100)
> on the same IRQ is working properly.

That's wired. Interrupt processing of the SJA1000 is done in the
interrupt context.

> Why CPU load inhibits hardware interrupts and what can be done about it?

Hm, what does "ip -d -s can0" report while you are producing CPU load
with the stress command above.

> Or should I suspect hardware malfunction?

More likely it's a bug.

Wolfgang.