[libvirt] [PATCH] docs: Add "PCI topology and hotplug" guidelines

[Andrea Bolognani]

On Wed, 2017-08-02 at 11:06 +0200, Marcin Juszkiewicz wrote:
> Thanks a lot for that documentation.

Glad you found it useful :)
Hopefully I can get it merged soon.

> At Linaro we use AArch64 servers to deploy VM machines (with OpenStack
> Newton or just libvirt) and issues with PCI hotplug came again and again.
> 
> https://bugs.linaro.org/show_bug.cgi?id=2819 is main one. It was created
> when we used libvirt 2.2.0 but now we are at 3.4.0 version and problem
> is finally debugged properly ;D
> 
> From my tests it looks like adding 9-10 pcie-root-port devices will
> handle our use - just have to convince OpenStack guys about it (or find
> a way around libvirt to get those by default).

The number of PCIe Root Ports provided by libvirt by default
is very unlikely to change: the current behavior, which is
consistent among aarch64/virt and x86_64/q35, has been
chosen specifically because it provides enough flexibility
for casual users without enforcing (too much of) a policy,
which is something that libvirt actively tries to avoid.

Adding extra PCIe Root Ports as appropriate for the specific
guest flavor is left as an exercise for the higher-level
management tool, in your case OpenStack.

-- 
Andrea Bolognani / Red Hat / Virtualization