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

From: David Gibson <[email-masked]>
Date: Thu, 10 Aug 2017 15:54:26 +1000

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:
> > 
> > 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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