From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:51768) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TbR5v-0003Lf-BH for qemu-devel@nongnu.org; Thu, 22 Nov 2012 02:21:08 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TbR5t-00049X-TE for qemu-devel@nongnu.org; Thu, 22 Nov 2012 02:21:07 -0500 Date: Thu, 22 Nov 2012 09:23:03 +0200 From: "Michael S. Tsirkin" Message-ID: <20121122072303.GA23260@redhat.com> References: <93E0DBC0-8611-4AF5-8035-B4AD409DD0D3@suse.de> <20121120122608.GA1756@redhat.com> <20121121005705.GM18362@truffula.fritz.box> <20121121113448.GA31911@redhat.com> <20121121123600.GV18362@truffula.fritz.box> <20121121131339.GA5730@redhat.com> <20121121132157.GW18362@truffula.fritz.box> <50ACD6AC.6030001@suse.de> <20121121152737.GC5730@redhat.com> <20121122022718.GY18362@truffula.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121122022718.GY18362@truffula.fritz.box> Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH 12/12] pseries: Generate unique LIOBNs for PCI host bridges List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: "qemu-ppc@nongnu.org List" , Alexander Graf , qemu-devel qemu-devel 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 > > > >>>>>>>>>> > > > >>>>>>>>>>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 > > > >>>>>>>>>>Signed-off-by: David Gibson > > > >>>>>>>>>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. > > If user wants to play with low level detail such as PHBs I don't see why > > it's not reasonable to require full specification. > > > > > How do we assign PCI slot IDs today when all you do is a -device? > > > This should probably follow the same scheme. > > > > > > > > > Alex > > > > What we do is find a first free slow. But it's exactly why I worry: > > changing pci addresses between qemu releases has been a source of pain > > and compatibility hassles in the past. > > The problem would be more manageable if you simply reserve some fixed > > addresses for internal use, like we reserve slots for VGA and IDE, > > though even that becomes a problem as we switch to q35. > > > > -- > 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