On Thu, Jan 14, 2016 at 07:20:32PM +0200, Marcel Apfelbaum wrote: > On 01/14/2016 05:37 PM, Michael S. Tsirkin wrote: > >On Thu, Jan 14, 2016 at 05:23:27PM +0200, Marcel Apfelbaum wrote: > >>On 01/14/2016 04:49 PM, Michael S. Tsirkin wrote: > >>>On Thu, Jan 14, 2016 at 03:30:41PM +0100, Laszlo Ersek wrote: > >>>>>2. The same as with pxb, disable Integrated End points for pxb-pcie. > >>>> > >>>>My vote, without a doubt. > >>> > >>>Yea, me too. > >>> > >>> > >>>On a related note: I wonder whether enough resources will be allocated > >>>to the bridge to actually make it possible to add devices by hotplug > >>>later. > >>> > >> > >>It works the same as with PXB, but now instead of having one internal > >>PCI-bridge, > >>we will have several switches/root ports. Each of them will get the minimum > >>MEM required by > >>PCI bridges, > > > >what does this mean? What if you add a bunch of devices > >with large memory BARs? They won't fit will they? > > > > Indeed, devices with over 1 MB (I think) BARs can't be hot-plugged. > This is a known design limitation. We can think of a way to handle this, > but the real reason we have multiple root bridges is to be able to > correlate an assigned device with a NUMA node. In this case the device > will be added more likely at boot time.
Ugh. That's pretty nasty, esp considering live migration pretty much requires hotplug ATM. > > I think the first step is to have *some* hot-plug support for pxb/pxb-pcie > with the current constraints, once it works we can think > of a way to make it work for devices with large BARs. > > Thanks, > Marcel Well OK but I suspect changes will require host/guest interface changes. Time enough before 2.6 but I would hate to release 2.6 with this limitation in place. And I'd like to mention a real pci express host won't have this issue I think as it is normally allocated a range of memory at boot time. > >>however the IO will be allocated only if at least one legacy device > >>will be present at boot time. (this is at least what SeaBIOS does, I am > >>going to check OVMF actions) > >> > >>Also related, checking that PCIe native hotplug works for devices behind > >>pxb-pcie bridges is my next step after I fix the current issue. > >> > >>Thanks, > >>Marcel > >> > >>> > >>>>> > >>>>>I am going to look at 1., maybe I is doable in a clean way. > >>>> > >>>>My vote: don't. :) > >>>> > >>>>Thanks > >>>>Laszlo > >>>> > >>>>>Thanks, > >>>>>Marcel > >>>>> > >>>>> > >>>>>[...]