On Fri, Nov 23, 2012 at 03:13:07PM +1100, David Gibson wrote: > On Thu, Nov 22, 2012 at 09:23:03AM +0200, Michael S. Tsirkin wrote: > > On Thu, Nov 22, 2012 at 01:27:18PM +1100, David Gibson wrote: > > > On Wed, Nov 21, 2012 at 05:27:37PM +0200, Michael S. Tsirkin wrote: > > > > On Wed, Nov 21, 2012 at 02:27:08PM +0100, Alexander Graf wrote: > > > > > On 11/21/2012 02:21 PM, David Gibson wrote: > > > > > >On Wed, Nov 21, 2012 at 03:13:39PM +0200, Michael S. Tsirkin wrote: > > > > > >>On Wed, Nov 21, 2012 at 11:36:00PM +1100, David Gibson wrote: > > > > > >>>On Wed, Nov 21, 2012 at 01:34:48PM +0200, Michael S. Tsirkin wrote: > > > > > >>>>On Wed, Nov 21, 2012 at 11:57:05AM +1100, David Gibson wrote: > > > > > >>>>>On Tue, Nov 20, 2012 at 02:26:09PM +0200, Michael S. Tsirkin > > > > > >>>>>wrote: > > > > > >>>>>>On Tue, Nov 20, 2012 at 10:27:11AM +0100, Alexander Graf wrote: > > > > > >>>>>>>On 19.11.2012, at 23:51, David Gibson wrote: > > > > > >>>>>>> > > > > > >>>>>>>>On Mon, Nov 19, 2012 at 05:34:12PM +0100, Alexander Graf > > > > > >>>>>>>>wrote: > > > > > >>>>>>>>>On 13.11.2012, at 03:47, David Gibson wrote: > > > > > >>>>>>>>> > > > > > >>>>>>>>>>From: Alexey Kardashevskiy<a...@ozlabs.ru> > > > > > >>>>>>>>>> > > > > > >>>>>>>>>>In future (with VFIO) we will have multiple PCI host > > > > > >>>>>>>>>>bridges on > > > > > >>>>>>>>>>pseries. Each one needs a unique LIOBN (IOMMU id). At the > > > > > >>>>>>>>>>moment we > > > > > >>>>>>>>>>derive these from the pci domain number, but the whole > > > > > >>>>>>>>>>notion of > > > > > >>>>>>>>>>domain numbers on the qemu side is bogus and in any case > > > > > >>>>>>>>>>they're not > > > > > >>>>>>>>>>actually uniquely allocated at this point. > > > > > >>>>>>>>>> > > > > > >>>>>>>>>>This patch, therefore uses a simple sequence counter to > > > > > >>>>>>>>>>generate > > > > > >>>>>>>>>>unique LIOBNs for PCI host bridges. > > > > > >>>>>>>>>> > > > > > >>>>>>>>>>Signed-off-by: Alexey Kardashevskiy<a...@ozlabs.ru> > > > > > >>>>>>>>>>Signed-off-by: David Gibson<da...@gibson.dropbear.id.au> > > > > > >>>>>>>>>I don't really like the idea of having a global variable just > > > > > >>>>>>>>>because our domain ID generation seems to not work as > > > > > >>>>>>>>>expected. Michael, any comments here? > > > > > >>>>>>>>Well, the patch I sent which changed domain id generation was > > > > > >>>>>>>>ignored. In any case, as I said, the whole concept of domain > > > > > >>>>>>>>numbers > > > > > >>>>>>>Michael? > > > > > >>>>>>This is user visible, right? > > > > > >>>>>>So IMHO we should have the user specify LIOBN through a > > > > > >>>>>>property, > > > > > >>>>>>rather than assign what's essentially a random value. > > > > > >>>>>Well, I can implement an override through a property, which > > > > > >>>>>could be > > > > > >>>>>useful in some circumstances. But we still need to have qemu > > > > > >>>>>generate > > > > > >>>>>unique defaults, rather than forcing it to be specified in every > > > > > >>>>>case. > > > > > >>>>I don't see why. > > > > > >>>>And if you want automatic defaults then they need to be generated > > > > > >>>>in a > > > > > >>>>way that does not depend on implementation detail such as order of > > > > > >>>>device initialization. > > > > > >>>Because requiring explicit unique liobns to be supplied whenever > > > > > >>>there > > > > > >>>is more than one PHB is horrible for usability. > > > > > >>We should make simple things simple and complex things possible. > > > > > >>More than one PHB seems like an advanced feature > > > > > >Not for pseries. On real hardware of this type, dozens of PHBs is > > > > > >routine. Plus, vfio passthrough is coming, we need at minimum one > > > > > >PHB > > > > > >for emulated devices and one for passthrough devices. > > > > > > > > > > Yeah, I second Davids opinion here. We need to make this easy for > > > > > users. > > > > > > > > I think users don't normally create PHBs. They request a disk, a network > > > > device, a pass-through device ... In this case if this requires > > > > more PHBs create them internally but I imagine this doesn't > > > > require any allocation scheme - simply set some address > > > > for virtual devices, some other one for assigned devices ... no? > > > > > > No. One PHB for passthrough and one for emulated is the minimum. > > > Since we don't emulated p2p bridges, > > > > Actually qemu does emulate p2p bridges. > > > > > each PHB can only support a small > > > number of PCI devices, so if enough PCI devices are requested, we will > > > still need to create - and assign numbers to - additional PHBs. > > > > Each PHB can support up to 32 slots right? This seems ample for > > a typical use. If you want many tens of devices you need to > > supply addresses manually, this looks reasonable to me. > > > > Allocating PHBs on the fly seems unencessarily tricky. > > I still think you're thinking far too much in terms of x86-like > guests. But, I guess, emulated PCI devices will be pretty rare, since > they're so slow anyway.
They are not very slow. My point is the reverse. Device assignment is pretty rare, assigning multiple devices even more rare. It should work but I don't see why we should increase maintainance burden to save the user ruynning qemu from CLI the trouble of specifying a single extra property in this advanced case. > But, what Alex was getting at is another factor I forgot. Because of > the way the PAPR PCI paravirtualized interfaces work, host devices > which are in different "partitionable endpoints" (roughly the minimum > granularity for safe isolation) must appear in different virtual PHBs > in the guest. So if we pass through a lot of PCI devices, we will > almost certainly need a lot of guest PHBs. One further point: physical systems normally don't let you hotplug PHBs. So if for non hotplug you auto-add PHBs, you end up treating hotplug and non hotplug devices differently from UI point of view this is nasty. Look, even if solution using a required property is less elegant for CLI use, it will work, won't it? So how about we merge it so that things work, and then we can discuss a patch on top that auto-generates this property? > -- > 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
