doc: add note on needing igb_uio for VF devices

Since the uio_pci_generic module requires that the device to which it is
being bound supports legacy interrupts, there can be problems using it
with VF devices. Add a note to the GSG doc to document this fact, and
provide information on loading igb_uio as a replacement.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>
Acked-by: Siobhan Butler <siobhan.a.butler@intel.com>

diff --git a/doc/guides/linux_gsg/build_dpdk.rst b/doc/guides/linux_gsg/build_dpdk.rst
index 255d6dc..5f0f3ae 100644 (file)
--- a/doc/guides/linux_gsg/build_dpdk.rst
+++ b/doc/guides/linux_gsg/build_dpdk.rst
@@ -166,7 +166,7 @@ Loading Modules to Enable Userspace IO for DPDK
 -----------------------------------------------
 
 To run any DPDK application, a suitable uio module can be loaded into the running kernel.
 -----------------------------------------------
 
 To run any DPDK application, a suitable uio module can be loaded into the running kernel.

-In most cases, the standard uio_pci_generic module included in the linux kernel
+In many cases, the standard uio_pci_generic module included in the linux kernel

 can provide the uio capability. This module can be loaded using the command
 
 .. code-block:: console
 can provide the uio capability. This module can be loaded using the command
 
 .. code-block:: console


@@ -174,7 +174,18 @@ can provide the uio capability. This module can be loaded using the command
     sudo modprobe uio_pci_generic
 
 As an alternative to the uio_pci_generic, the DPDK also includes the igb_uio
     sudo modprobe uio_pci_generic
 
 As an alternative to the uio_pci_generic, the DPDK also includes the igb_uio

-module which can be found in the kmod subdirectory referred to above.
+module which can be found in the kmod subdirectory referred to above. It can
+be loaded as shown below:
+
+.. code-block:: console
+
+    sudo modprobe uio
+    sudo insmod kmod/igb_uio.ko
+
+.. note::
+
+    For some devices which lack support for legacy interrupts, e.g. virtual function
+    (VF) devices, the igb_uio module may be needed in place of uio_pci_generic.

 
 Since DPDK release 1.7 onward provides VFIO support, use of UIO is optional
 for platforms that support using VFIO.
 
 Since DPDK release 1.7 onward provides VFIO support, use of UIO is optional
 for platforms that support using VFIO.