Re: [Xen-devel] [question] what's the purpose of smp_send_event_check_mask?

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 19/01/2012 09:02, "Kai Huang" <mail.kai.huang@xxxxxxxxx> wrote:

> Hi,
> 
> I see cpu_raise_softirq calls smp_send_event_check_mask after setting
> softirq bit for target CPU if target CPU is not the current CPU. I
> thought smp_send_event_check_mask will send IPI to target CPU and then
> trigger target CPU to run pending irq, but seems
> smp_send_event_check_mask does nothing but jast ACK the IPI. So what's
> the purpose of this function? Why do we need this function?

Xen always checks softirqs on return from interrupt context to guest
context, and also in its idle loopon wakeup. Hence the event_check interrupt
handler itself doesn't need to do anything.

> BTW, would someone gives me some knowledge when will the pending irqs
> be triggered to run after setting up the pending bits? Seems normally
> they are called asynchronously.

Yes, of course it's asynchronous, the smp_send_event_check_mask interrupt is
just to make sure it happens "soon".

 -- Keir

> Thanks in advance!
> 
> -cody
> 
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