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Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines |
Date: |
Tue, 4 Oct 2016 15:59:11 +0100 |
User-agent: |
Mutt/1.7.0 (2016-08-17) |
On Mon, Sep 05, 2016 at 06:24:48PM +0200, Laszlo Ersek wrote:
> On 09/01/16 15:22, Marcel Apfelbaum wrote:
> > +2.3 PCI only hierarchy
> > +======================
> > +Legacy PCI devices can be plugged into pcie.0 as Integrated Devices or
> > +into DMI-PCI bridge. PCI-PCI bridges can be plugged into DMI-PCI bridges
> > +and can be nested until a depth of 6-7. DMI-BRIDGES should be plugged
> > +only into pcie.0 bus.
> > +
> > + pcie.0 bus
> > + ----------------------------------------------
> > + | |
> > + ----------- ------------------
> > + | PCI Dev | | DMI-PCI BRIDGE |
> > + ---------- ------------------
> > + | |
> > + ----------- ------------------
> > + | PCI Dev | | PCI-PCI Bridge |
> > + ----------- ------------------
> > + | |
> > + ----------- -----------
> > + | PCI Dev | | PCI Dev |
> > + ----------- -----------
>
> Works for me, but I would again elaborate a little bit on keeping the
> hierarchy flat.
>
> First, in order to preserve compatibility with libvirt's current
> behavior, let's not plug a PCI device directly in to the DMI-PCI bridge,
> even if that's possible otherwise. Let's just say
>
> - there should be at most one DMI-PCI bridge (if a legacy PCI hierarchy
> is required),
Why do you suggest this ? If the guest has multiple NUMA nodes
and you're creating a PXB for each NUMA node, then it looks valid
to want to have a DMI-PCI bridge attached to each PXB, so you can
have legacy PCI devices on each NUMA node, instead of putting them
all on the PCI bridge without NUMA affinity.
> - only PCI-PCI bridges should be plugged into the DMI-PCI bridge,
What's the rational for that, as opposed to plugging devices directly
into the DMI-PCI bridge which seems to work ?
Regards,
Daniel
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- Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines,
Daniel P. Berrange <=
- Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines, Laszlo Ersek, 2016/10/04
- Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines, Laine Stump, 2016/10/04
- Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines, Laszlo Ersek, 2016/10/04
- Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines, Laine Stump, 2016/10/04
- Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines, Alex Williamson, 2016/10/04
- Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines, Andrea Bolognani, 2016/10/10
- Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines, Marcel Apfelbaum, 2016/10/10
- Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines, Andrea Bolognani, 2016/10/11
- Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines, Laszlo Ersek, 2016/10/04
- Re: [Qemu-devel] [PATCH RFC] docs: add PCIe devices placement guidelines, Laine Stump, 2016/10/04