Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency?

[Peter Maydell]

On 15 June 2015 at 16:05, Alex Züpke <address@hidden> wrote:
> Am 15.06.2015 um 16:51 schrieb Peter Maydell:
>> On 15 June 2015 at 15:44, Alex Züpke <address@hidden> wrote:
>>> Am 12.06.2015 um 20:03 schrieb Peter Maydell:
>>>> Probably the best approach would be to have something in
>>>> arm_cpu_set_irq() which says "if we are CPU X and we've
>>>> just caused an interrupt to be set for CPU Y, then we
>>>> should ourselves yield back to the main loop".
>>>>
>>>> Something like this, maybe, though I have done no more testing
>>>> than checking it doesn't actively break kernel booting :-)
>>>
>>>
>>> Thanks! One more check for "level" is needed to get it work:
>>
>> What happens without that? It's reasonable to have it,
>> but extra cpu_exit()s shouldn't cause a problem beyond
>> being a bit inefficient...
>
> The emulation get's stuck, for whatever reason I don't understand.

I'm beginning to suspect that your guest code has a race
condition in it, such that if the other CPU runs at a
point you weren't expecting it to then you end up
deadlocking or otherwise running into a bug in your guest.

In particular, I see the emulation getting stuck even without
this patch to arm_cpu_set_irq().

-- PMM