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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Laszlo Ersek <lersek@redhat.com>,
	Marcel Apfelbaum <marcel.apfelbaum@gmail.com>,
	Zihan Yang <whois.zihan.yang@gmail.com>,
	qemu-devel@nongnu.org, Igor Mammedov <imammedo@redhat.com>,
	Eric Auger <eauger@redhat.com>, Drew Jones <drjones@redhat.com>,
	Wei Huang <wei@redhat.com>
Subject: Re: [Qemu-devel] [RFC 3/3] acpi-build: allocate mcfg for multiple host bridges
Date: Wed, 23 May 2018 02:38:52 +0300	[thread overview]
Message-ID: <20180523005048-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20180522154741.3939d1e0@w520.home>

On Tue, May 22, 2018 at 03:47:41PM -0600, Alex Williamson wrote:
> On Wed, 23 May 2018 00:44:22 +0300
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Tue, May 22, 2018 at 03:36:59PM -0600, Alex Williamson wrote:
> > > On Tue, 22 May 2018 23:58:30 +0300
> > > "Michael S. Tsirkin" <mst@redhat.com> wrote:   
> > > >
> > > > It's not hard to think of a use-case where >256 devices
> > > > are helpful, for example a nested virt scenario where
> > > > each device is passed on to a different nested guest.
> > > >
> > > > But I think the main feature this is needed for is numa modeling.
> > > > Guests seem to assume a numa node per PCI root, ergo we need more PCI
> > > > roots.  
> > > 
> > > But even if we have NUMA affinity per PCI host bridge, a PCI host
> > > bridge does not necessarily imply a new PCIe domain.  
> > 
> > What are you calling a PCIe domain?
> 
> Domain/segment
> 
> 0000:00:00.0
> ^^^^ This

Right. So we can thinkably have PCIe root complexes share an ACPI segment.
I don't see what this buys us by itself.

> Isn't that the only reason we'd need a new MCFG section and the reason
> we're limited to 256 buses?  Thanks,
> 
> Alex

I don't know whether a single MCFG section can describe multiple roots.
I think it would be certainly unusual.

-- 
MST

  parent reply	other threads:[~2018-05-22 23:38 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-20  7:28 [Qemu-devel] [RFC 0/3] pci_expander_brdige: Put pxb host bridge into separate pci domain Zihan Yang
2018-05-20  7:28 ` [Qemu-devel] [RFC 1/3] pci_expander_bridge: reserve enough mcfg space for pxb host Zihan Yang
2018-05-21 11:03   ` Marcel Apfelbaum
2018-05-22  5:59     ` Zihan Yang
2018-05-22 18:47       ` Marcel Apfelbaum
2018-05-20  7:28 ` [Qemu-devel] [RFC 2/3] pci: Link pci_host_bridges with QTAILQ Zihan Yang
2018-05-21 11:05   ` Marcel Apfelbaum
2018-05-22  5:59     ` Zihan Yang
2018-05-22 18:39       ` Marcel Apfelbaum
2018-05-20  7:28 ` [Qemu-devel] [RFC 3/3] acpi-build: allocate mcfg for multiple host bridges Zihan Yang
2018-05-21 11:53   ` Marcel Apfelbaum
2018-05-22  6:03     ` Zihan Yang
2018-05-22 18:43       ` Marcel Apfelbaum
2018-05-22  9:52     ` Laszlo Ersek
2018-05-22 19:01       ` Marcel Apfelbaum
2018-05-22 19:51         ` Laszlo Ersek
2018-05-22 20:58           ` Michael S. Tsirkin
2018-05-22 21:36             ` Alex Williamson
2018-05-22 21:44               ` Michael S. Tsirkin
2018-05-22 21:47                 ` Alex Williamson
2018-05-22 22:00                   ` Laszlo Ersek
2018-05-22 23:38                   ` Michael S. Tsirkin [this message]
2018-05-23  4:28                     ` Alex Williamson
2018-05-23 14:25                       ` Michael S. Tsirkin
2018-05-23 14:57                         ` Alex Williamson
2018-05-23 15:01                           ` Michael S. Tsirkin
2018-05-23 16:50                         ` Marcel Apfelbaum
2018-05-22 21:17           ` Alex Williamson
2018-05-22 21:22             ` Michael S. Tsirkin
2018-05-22 21:58               ` Laszlo Ersek
2018-05-22 21:50             ` Laszlo Ersek
2018-05-23 17:00             ` Marcel Apfelbaum
2018-05-22 22:42           ` Laszlo Ersek
2018-05-22 23:40             ` Michael S. Tsirkin
2018-05-23  7:32               ` Laszlo Ersek
2018-05-23 11:11                 ` Zihan Yang
2018-05-23 12:28                   ` Laszlo Ersek
2018-05-23 17:23                     ` Marcel Apfelbaum
2018-05-24  9:57                     ` Zihan Yang
2018-05-23 17:33                   ` Marcel Apfelbaum
2018-05-24 10:00                     ` Zihan Yang
2018-05-23 17:11                 ` Marcel Apfelbaum
2018-05-23 17:25                   ` Laszlo Ersek
2018-05-28 11:02                 ` Laszlo Ersek
2018-05-21 15:23 ` [Qemu-devel] [RFC 0/3] pci_expander_brdige: Put pxb host bridge into separate pci domain Marcel Apfelbaum
2018-05-22  6:04   ` Zihan Yang

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