Re: [PATCH 02/10] powerpc/xive: guest exploitation of the XIVE interrupt controller

On Thu, Aug 10, 2017 at 02:46:00PM +1000, Benjamin Herrenschmidt wrote:

On Thu, 2017-08-10 at 14:28 +1000, David Gibson wrote:

quoted

Also, will POWER9 always have doorbells?  In which case you could
reduce it to 3 options.

The problem with doorbells on POWER9 guests is that they may have
to trap and be emulated by the hypervisor, since the guest threads
on P9 don't have to match the HW threads of the core.

Thus it's quite possible that using XIVE for IPIs is actually faster
than doorbells in that case.

Ok, well unless there's a compelling reason to use doorbells you can
instead make it 3 cases with POWER9 never using doorbells.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
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