After some research I have ended up now in APC'c thread handling (see code
snipped below, out of ksrc/arch/generic/hal.c). From my point of view there
could be occur the "lost wakeup problem". That means in detail that
rthal_kicker() calls wakeup when rthal_apc_thread() has returned from
rthal_apc_handler() but not yet called set_current_state(). After that, when
kicker has finished, the APC thread calls set_current_state() and goes to
sleep. Thus, the wakeup is lost. Or do I overlook something? Maybe we should
use a waitqueue here?
static int rthal_apc_thread(void *data)
{
unsigned cpu = (unsigned)(unsigned long)data;
set_cpus_allowed(current, cpumask_of_cpu(cpu));
sigfillset(¤t->blocked);
current->flags |= PF_NOFREEZE;
/* Use highest priority here, since some apc handlers might
require to run as soon as possible after the request has been
pended. */
rthal_setsched_root(current, SCHED_FIFO, MAX_RT_PRIO - 1);
while (!kthread_should_stop()) {
set_current_state(TASK_INTERRUPTIBLE);
schedule();
rthal_apc_handler(0, NULL);
}
__set_current_state(TASK_RUNNING);
return 0;
}
void rthal_apc_kicker(unsigned virq, void *cookie)
{
wake_up_process(rthal_apc_servers[smp_processor_id()]);
}
Regards,
Christoph
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