full no_hz: how works arch_irq_work_raise() with tick off on generic implementation

From: Sebastian Andrzej Siewior
Date: Mon Mar 09 2015 - 10:09:34 EST

I just stumbled over this in -RT. The code:

87 bool irq_work_queue(struct irq_work *work)
88 {
96 /* If the work is "lazy", handle it from next tick if any */
97 if (work->flags & IRQ_WORK_LAZY) {
98 if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
99 tick_nohz_tick_stopped())
100 arch_irq_work_raise();
101 } else {
102 if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
103 arch_irq_work_raise();
104 }
109 }

so what I asked myself: What happens if the CPU is in NO_HZ mode with
the tick off and you invoke arch_irq_work_raise() on an architecture
without a special IRQ_WORK interrupt?
And why you don't this tick_nohz_tick_stopped() check for the
Wouldn't it be a easier for your full NO_HZ code to simply run in the
hardirq exit path instead of using irq_work?

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