[LITMUS^RT] Supporting Job Aborts

[Björn Brandenburg]

On 07.09.2012, at 21:29, Glenn Elliott <gelliott at cs.unc.edu> wrote:

> It sounds like the kernel still has to be modified to perform the budget changes.

For what you described initially (signal on budget overrun), no. For slack donation, yes of course. But it's likely a lot easier than introducing new signals and hacking / removing the user space trampoline.

>  How does the kernel know which timer instance associated with a task is the one that the task set up, at the application level, to perform the budget timing?  In all likelihood, there would just be one timer (especially just one with the ITIMER_VIRTUAL), but we still can't be entirely sure, right?

That's why I said I'd flag the timer as being special. Of course, no such support exists in standard Linux and would have to be added. Still, that's likely not that hard—just add a setitimer2() syscall that takes an additional flags parameter and proxies the rest to the normal itimer machinery.

Anyway, I probably don't fully understand what you have planned with this in the long term; my point is mainly that similar mechanisms already exist and that hacking them is likely simpler than doing low-level signal delivery work.

- Björn