Re: [Xenomai-help] Handling Linux Signals in primary domain context

[Philippe Gerum <rpm@xenomai.org>]

On Tue, 2010-06-01 at 15:50 +0200, Tschaeche IT-Services wrote:
> Hi,
> 
> we have the following scenario:
> 
> A high priority periodic primary domain task (H), which calls
> rt_task_suspend(L) in each even period and rt_task_resume(L)
> in each odd period on a low priority primary domain task (L).
> L-task consumes all available CPU resources (while(1)).
> Thus, the rest of each cycle (after H has got the CPU) is used
> alternately by L-task, ROOT-task, L-task,...
> 
> In our debugging implementation, we send a SIGTRAP to L-task.
> H-task recognizes this by reporting EINTR when calling rt_task_suspend(L).
> But, the while(1) in L-task is not interrupted although there is a SIGTRAP
> pending.

Using SIGTRAP will badly conflict with GDB. Hope this is ok.

> 
> Our workaround could be, to send a rt_signal when rt_task_suspend()
> returns EINTR and, then, in the rt-signal handler migrate L-task
> to secondary domain (calling rt_task_set_mode(T_PRIMARY,0))
> initiating the Linux scheduler, which, then, initiates the SIGTRAP handling
> in secondary domain context.
> 
> Is there a simpler way to get primary domain tasks interrupted
> by Linux signals? Xenomai already knows about the pending signal
> and, maybe, could initiate the secondary domain switch on a primary scheduler
> event.

Not in the absence of syscall. We thought about this once already, when
considering how a watchdog preempting a runaway task in primary mode
could force a secondary mode switch: there is no sane and easy solution
to this unfortunately.

If the basic idea is about throttling the activity of the L-task, then
you could use the sporadic server policy (enabled via
pthread_setschedparam_ex()).

> 
> Thanks,
> 
> 	Olli
> 
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-- 
Philippe.