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Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers |
Date: |
Thu, 4 Aug 2011 22:14:15 +0300 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Thu, Aug 04, 2011 at 07:00:38PM +1000, David Gibson wrote:
> On Wed, Aug 03, 2011 at 04:28:33PM +0300, Michael S. Tsirkin wrote:
> > On Tue, Aug 02, 2011 at 12:15:22AM +1000, David Gibson wrote:
> > > On Mon, Aug 01, 2011 at 05:03:18PM +0300, Michael S. Tsirkin wrote:
> > > > On Mon, Aug 01, 2011 at 11:33:37PM +1000, David Gibson wrote:
> > > > > On Mon, Aug 01, 2011 at 01:10:38PM +0300, Michael S. Tsirkin wrote:
> > > > > > On Mon, Aug 01, 2011 at 04:51:02PM +1000, David Gibson wrote:
> > > > > > > qemu already almost supports PCI domains; that is, several
> > > > > > > entirely
> > > > > > > independent PCI host bridges on the same machine. However, a bug
> > > > > > > in
> > > > > > > pci_bus_new_inplace() means that every host bridge gets assigned
> > > > > > > domain
> > > > > > > number zero and so can't be properly distinguished. This patch
> > > > > > > fixes the
> > > > > > > bug, giving each new host bridge a new domain number.
> > > > > > >
> > > > > > > Signed-off-by: David Gibson <address@hidden>
> > > > > >
> > > > > > OK, but I'd like to see the whole picture.
> > > > > > How does the guest detect multiple domains,
> > > > > > and how does it access them?
> > > > >
> > > > > For the pseries machine, which is what I'm concerned with, each host
> > > > > bridge is advertised through the device tree passed to the guest.
> > > >
> > > > Could you explain please?
> > > > What generates the device tree and passes it to the guest?
> > >
> > > In the case of the pseries machine, it is generated from hw/spapr.c
> > > and loaded into memory for use by the firmware and/or the kernel.
> > >
> > > > > That gives the necessary handles and addresses for accesing config
> > > > > space and memory and IO windows for each host bridge.
> > > >
> > > > I see. I think maybe a global counter in the common code
> > > > is not exactly the best solution in the general case.
> > >
> > > Well, which general case do you have in mind. Since by definition,
> > > PCI domains are entirely independent from each other, domain numbers
> > > are essentially arbitrary as long as they're unique - simply a
> > > convention which makes it easier to describe which host bridge devices
> > > belong on. I don't see an obvious approach which is better than a
> > > global counter, or least not one that doesn't involve a significant
> > > rewrite of the PCI subsystem.
> >
> > OK, let's make sure I understand. On your system 'domain numbers'
> > are completely invisible to the guest, right? You only need them to
> > address devices on qemu monitor ...
>
> Well.. the qemu domain number is not officially visible to the guest.
> However the handles that are visible to the guest will need to be
> derived from some sort of unique domain number.
Interesting. How does it work with your patch?
> > For that, I'm trying to move away from using a domain number. Would
> > it be possible to simply give bus an id, and use bus=<id> instead?
>
> It might be. In this case we should remove the domain numbers (as
> used by pci_find_domain()) from qemu entirely,
Or at least, move to acpi-specific code.
> since they are broken
I agree, they are broken.
> as they stand without this patch.
>
> > BTW, how does a linux guest number domains?
> > Would it make sense to match that?
>
> I'll look into it. It would be nice to have them match, obviously but
> I'm not sure if there will be a way to do this that's both reasonable
> and robust. I suspect they will match already though not in a
> terribly robust way, at least for the pseries machine, becuase qemu
> will create the host bridge nodes in the same order as domain number,
> and I suspect Linux will just allocate domain numbers sequentially in
> that same order.
If the order of things in the tree matters for some guests, we should
give users a way to control that order, or at least make
the order robust.
> --
> 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
- [Qemu-devel] [PATCH] Correctly assign PCI domain numbers, David Gibson, 2011/08/01
- Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers, Isaku Yamahata, 2011/08/01
- Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers, Michael S. Tsirkin, 2011/08/01
- Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers, David Gibson, 2011/08/01
- Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers, Michael S. Tsirkin, 2011/08/01
- Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers, David Gibson, 2011/08/01
- Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers, Michael S. Tsirkin, 2011/08/03
- Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers, David Gibson, 2011/08/04
- Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers, Michael S. Tsirkin, 2011/08/10
- Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers, David Gibson, 2011/08/11
Re: [Qemu-devel] [Qemu-trivial] [PATCH] Correctly assign PCI domain numbers, Stefan Hajnoczi, 2011/08/03
Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers, David Gibson, 2011/08/09