Re: [libvirt] [PATCH v4 4/4] auto-create pci-bridge controller info

在 2013-03-05二的 10:36 +0000，Daniel P. Berrange写道： > On Mon, Mar 04, 2013 at 02:39:40PM -0500, Laine Stump wrote: > > On 03/04/2013 11:51 AM, Ján Tomko wrote: > > > On 02/19/13 03:25, liguang wrote: > > >> if some devices specify a pci bus number that > > >> haven't been defined by a pci-bridge controller > > >> then fill the required correct controller info > > >> silently. > > >> > > >> Acked-by: Daniel P. Berrange <berrange(a)redhat.com&gt; > > >> Signed-off-by: liguang <lig.fnst(a)cn.fujitsu.com&gt; > > >> --- > > > This will only add bridges for the explictly mentioned buses, which > > > would mean we could have buses 0 and 6 with no buses between them. > > > Maybe we should add them the way we add disk controllers - find the > > > highest index and add all bridges with indexes from 1 to max. > > > > But each pci bridge device takes up another slot, which we may not want > > to give up. (Although arguably, once we have pci-bridge devices, we can > > create as many slots as we like :-) > > > > > > Is there some advantage to having all the buses filled in (other than > > similarity to what's done for other types of controllers)? > > > > > It would be nice if we could add pci bridges even when there weren't any > > > specified in the XML, but there are too many PCI devices. I don't know > > > what would be the nicest way to do that. > > > > If we auto-assign addresses for un-addressed devices first (your recent > > patches did that, right? I forget the status of those), *then* > > auto-create the required bridges (which themselves will need an > > auto-assigned address), that should just happen. > > > > Of course, if we do that, then we won't have reserved any slots on bus 0 > > for even a single pci-bridge device, so we'll fail. Is the proper way > > out of this to always reserve one (or maybe two, for good measure) slots > > on any given bus to be used only for bridges? That way no matter how out > > of hand things get, we'll always have a place we can add another bus. > > (In the case of *lots* of devices, I assume that a device on a nested > > PCI bridge would be less efficient, and may have some other limitations, > > but it would be better than nothing. And if the admin was really > > concerned about that, they could modify their config to explicitly place > > several bridges directly on bus 0) > > You'd have todo a 2 pass assignment. First count the number of devices > that need to have PCI addresses assigned. Then create the required > number of bridges, then assign the addresses. > > All this time though, bear in mind that auto-address assignment is just > a convenience. At some point we are well within our right to stop and > say this is as good as its going to get, you must do address assignment > if the app if you want something more clever. > > > This also brings up the fact that we need to deal with the possibility > > of all buses being full during hotplug - when that happens I suppose we > > will also want to auto-add a pci bridge. > > Well if buses are all full, there's no where to hook in the bridge :-) > So you need to do that before filling up, or just say this is out of > scope and the app must explicitly plug a bridge if they want more space. Hmm, it's good point that haven't been considered by me, so, do I have to hack into device hot-plug to know if bus slot is almost exhausted and decide whether add pci-bridge or not? or, just let user bear in mind that?

> > > Daniel > -- > |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| > |: http://libvirt.org -o- http://virt-manager.org :| > |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| > |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| > > -- > libvir-list mailing list > libvir-list(a)redhat.com > https://www.redhat.com/mailman/listinfo/libvir-list -- libvir-list mailing list libvir-list(a)redhat.com https://www.redhat.com/mailman/listinfo/libvir-list