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

- From: David Gibson \<hidden\>
- Date: 2017-08-10 06:10:26 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2017/08/9499014
- Thread: https://ratatoskr.run/linuxppc-dev/2017/08/9498955/t.md

```text
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_!
http://www.ozlabs.org/~dgibson
```

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