On Fri, Jan 06, 2017 at 06:34:29PM +0100, Andrea Bolognani wrote: > [Added Laine to CC, fixed qemu-devel address] > > On Thu, 2017-01-05 at 16:46 +1100, David Gibson wrote: > [...] > > * To allow for hotplugged devices, libvirt should also add a number > > of additional, empty vPHBs (the PAPR spec allows for hotplug of > > PHBs, but this is not yet implemented in qemu). > > "A number" here will have to mean "one", same number of > empty PCIe Root Ports libvirt will add to a newly-defined > q35 guest. Umm.. why? > > When hotplugging > > a new device (or PE) libvirt should locate a vPHB which doesn't > > currently contain anything. > > This will need to be a PHB-specific behavior, because at the > moment libvirt will happily pick one of the empty slots in > an existing PHB. Exactly. Well, whether it's PHB model specific or machine type specific is up to you really. We can only have PAPR PHBs on a PAPR machine type, so it's kind of arbitrary. > > > * libvirt should only (automatically) add PHBs - never root ports or > > other PCI to PCI bridges > > > > In order to handle migration, the vPHBs will need to be represented in > > the domain XML, which will also allow the user to override this > > topology if they want. > > We'll have to decide how to represent them in the XML, but > that's basically your average bikeshedding. Right. Maybe we'd best get started with it, in the hopes of finishing it in the forseeable future. > Overall, the plan seems entirely reasonable to me. > > It's pretty clear at this point that pseries guest are > different enough in their handling of PCI that none of > the address allocation algorithms currently implemented > in libvirt could be quite adapted to work with it, so > a custom one is in order. Yes, that was my conclusion as well. -- 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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