void softlockup_tick(void) {
int this_cpu = smp_processor_id();
unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
unsigned long print_timestamp;
struct pt_regs *regs = get_irq_regs();
unsigned long now;
/* Is detection switched off? */
if (!per_cpu(watchdog_task, this_cpu) || softlockup_thresh <= 0) {
/* Be sure we don't false trigger if switched back on */
if (touch_timestamp)
per_cpu(touch_timestamp, this_cpu) = 0;
return;
}
if (touch_timestamp == 0) {
__touch_softlockup_watchdog();
return;
}
print_timestamp = per_cpu(print_timestamp, this_cpu);
/* report at most once a second */
if (print_timestamp == touch_timestamp || did_panic)
return;
/* do not print during early bootup: */
if (unlikely(system_state != SYSTEM_RUNNING)) { __touch_softlockup_watchdog();
return;
}
now = get_timestamp(this_cpu);
/*
* Wake up the high-prio watchdog task twice per
* threshold timespan.
*/
if (now > touch_timestamp + softlockup_thresh/2)
wake_up_process(per_cpu(watchdog_task, this_cpu));
/* Warn about unreasonable delays: */
if (now <= (touch_timestamp + softlockup_thresh))
return;
per_cpu(print_timestamp, this_cpu) = touch_timestamp;
spin_lock(&print_lock);
printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n", this_cpu, now - touch_timestamp, current->comm, task_pid_nr(current)); print_modules();
print_irqtrace_events(current);
if (regs)
show_regs(regs);
else
dump_stack();
spin_unlock(&print_lock);
if (softlockup_panic)
panic("softlockup: hung tasks");
}
请详细注释一下该函数的执行流程，该函数是怎样被调用的？主要功能是什么？另外per_cpu()的功能是什么？
望高手赐教，十分感谢！