Kernel Summit 2006: Realtime [LWN.net]

Kernel Summit 2006: Realtime

Posted Jul 25, 2006 20:47 UTC (Tue) by obobo (guest, #684)
Parent article: Kernel Summit 2006: Realtime

> One outstanding issue is recovery when a realtime task goes out of control...

In embedded systems, it is common to use a watchdog for this situation. It would seem to be straightforward to construct one using a highest priority task (doing a timed wait on a semaphore), and a low priority task which periodically posts to that semaphore. If the semwait times out, the watchdog task takes appropriate action against the offending process.

Any reason not to foist it off onto user space like that?

-Bill

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Kernel Summit 2006: Realtime

Posted Jul 31, 2006 16:44 UTC (Mon) by Blaisorblade (guest, #25465) [Link]

There is already a soft watchdog in the kernel almost exactly like that - the only difference from your proposal is that instead of one high-priority process it is the timer interrupt to do the check; I also think that since the time interrupt should remain a raw interrupt without a task checking for it (it's used for the scheduler) it is the same thing.

And both things aren't safe when a process disables interrupts but that's not interesting (you really need a hardware watchdog for that).