From: Rafal Kozik <r...@semihalf.com>
ENAv2 hardware provides Low Latency Queue v2 (LLQv2). It needs kernel
PCI driver to support write combining (WC). This patch add information
how to use it with igb_uio and vfio-pci drivers.
Signed-off-by: Rafal Kozik <r...@semihalf.com>
Acked-by: Michal Krawczyk <m...@semihalf.com>
---
doc/guides/nics/ena.rst | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/doc/guides/nics/ena.rst b/doc/guides/nics/ena.rst
index 9f0a650..80da4b6 100644
--- a/doc/guides/nics/ena.rst
+++ b/doc/guides/nics/ena.rst
@@ -183,10 +183,22 @@ Prerequisites
#. Prepare the system as recommended by DPDK suite. This includes environment
variables, hugepages configuration, tool-chains and configuration.
-#. ENA PMD can operate with ``vfio-pci`` or ``igb_uio`` driver.
+#. ENA PMD can operate with ``vfio-pci``(*) or ``igb_uio`` driver.
+
+ (*) ENAv2 hardware supports Low Latency Queue v2 (LLQv2). This feature
+ reduces the latency of the packets by pushing the header directly through
+ the PCI to the device, before the DMA is even triggered. For proper work
+ kernel PCI driver must support write combining (WC). In mainline version of
+ ``igb_uio`` (in DPDK repo) it must be enabled by loding module with
+ ``wc_activate=1`` flag (example below). However, mainline's vfio-pci
+ driver in kernel doesn't have WC support yet (planed to be added).
+ If vfio-pci used user should be either turn off ENAv2 (to avoid performance
+ impact) or recompile vfio-pci driver with patch provided in
+ `amzn-github
<https://github.com/amzn/amzn-drivers/tree/master/userspace/dpdk/enav2-vfio-patch>`_.
#. Insert ``vfio-pci`` or ``igb_uio`` kernel module using the command
- ``modprobe vfio-pci`` or ``modprobe igb_uio`` respectively.
+ ``modprobe vfio-pci`` or ``modprobe uio; insmod igb_uio.ko wc_activate=1``
+ respectively.
#. For ``vfio-pci`` users only:
Please make sure that ``IOMMU`` is enabled in your system,
--
2.7.4
