On 08/10/2017 07:54 AM, David Gibson wrote: > 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.
yes I suppose we could improve things for XIVE. For XICS, there are another 3 backends behind icp_ops->cause_ipi. I need to take a look. Thanks, C.