[vfio-users] VFIO 128 byte TLP size?

[Alex Williamson]

On Fri, 9 Mar 2018 18:03:14 +0100
Oliver Heid <Oliver.Heid at h-next.de> wrote:

> Does VFIO somehow limit PCIe TLP size to 128 bytes on virtualized 
> devices? In our case MaxPayload = MaxReadReq = 256 bytes in PCI config, 
> and we use 4k aligned base addresses and do not cross 4k boundaries, but 
> actual package size is only 128B. Any idea how to get 256 byte TLPs?

See:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/vfio/pci/vfio_pci_config.c?id=523184972b282cd9ca17a76f6ca4742394856818
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/vfio/pci/vfio_pci_config.c?id=cf0d53ba4947aad6e471491d5b20a567cbe92e56

And to tune the host MPS settings:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/kernel-parameters.txt#n3058

Suggestions for improvement welcome.  Thanks,

Alex