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A typical cloud provider SR-IOV use case is to create many VFs for use by guest VMs. The VFs may not be assigned to a VM until a customer requests a VM of a certain size, e.g., number of CPUs. A VF may need MSI-X vectors proportional to the number of CPUs in the VM, but there is no standard way to change the number of MSI-X vectors supported by a VF. Some Mellanox ConnectX devices support dynamic assignment of MSI-X vectors to SR-IOV VFs. This can be done by the PF driver after VFs are enabled, and it can be done without affecting VFs that are already in use. The hardware supports a limited pool of MSI-X vectors that can be assigned to the PF or to individual VFs. This is device-specific behavior that requires support in the PF driver. Add a read-only "sriov_vf_total_msix" sysfs file for the PF and a writable "sriov_vf_msix_count" file for each VF. Management software may use these to learn how many MSI-X vectors are available and to dynamically assign them to VFs before the VFs are passed through to a VM. If the PF driver implements the ->sriov_get_vf_total_msix() callback, "sriov_vf_total_msix" contains the total number of MSI-X vectors available for distribution among VFs. If no driver is bound to the VF, writing "N" to "sriov_vf_msix_count" uses the PF driver ->sriov_set_msix_vec_count() callback to assign "N" MSI-X vectors to the VF. When a VF driver subsequently reads the MSI-X Message Control register, it will see the new Table Size "N". Link: https://lore.kernel.org/linux-pci/20210314124256.70253-2-leon@kernel.org Acked-by: Bjorn Helgaas <bhelgaas@google.com> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.