On 15/09/2026 15:29, Peter Krempa wrote:
On Tue, Sep 15, 2026 at 13:46:16 +0000, David Vrabel wrote:
When a VM has been assigned a number of PCIe devices behind a common
PCIe switch and the VM intends to use peer-to-peer (P2P) transfers
between the devices, it is useful to be able to more report the
apparent PCIe bandwidth so it reflects the real handwidth of the
underlying hardware. This allows software in the VM (such as NCCL[1])
to make better decisions about whether to use P2P or not.
Newer versions[1] of QEMU will support new upstream and downstream
port models that have configurable speed and width properties and
extend the existing root port model to support the same options.
If supported by QEMU, prefer the new upstream and downstream port
models, and support new attributes to set the speed and width.
These are not merged upstream. Patches you propose here will need to
wait until that happens.
...> Once your qemu patches get merged to the master branch upstream let me
know and I'll regenerate the capability dump so that the property is
properly present. Do not change it in existing dump files.
The QEMU changes have now been merged[1]. Can you refresh the capability
dump, please?
David
[1]
https://gitlab.com/qemu-project/qemu/-/commit/73962cc5f06a3f946fe58fb227600c113cb9c90d
[2]
https://gitlab.com/qemu-project/qemu/-/commit/432b3f707a3c16288338594bb03df3db70cc9b53
