[dpdk-dev] [PATCH] doc: add driver limitation for vhost dequeue zero copy

[Junjie Chen <junjie.j.chen@intel.com>]

In vhost-switch example, when binding nic to vfio-pci, dequeue zero
copy cannot work in VM2NIC mode due to no iommu dma mapping is setup
for guest memory currently.

Signed-off-by: Junjie Chen <junjie.j.chen@intel.com>
---
 doc/guides/sample_app_ug/vhost.rst | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/doc/guides/sample_app_ug/vhost.rst b/doc/guides/sample_app_ug/vhost.rst
index a4bdc6a..1591a31 100644
--- a/doc/guides/sample_app_ug/vhost.rst
+++ b/doc/guides/sample_app_ug/vhost.rst
@@ -147,7 +147,10 @@ retries on an RX burst, it takes effect only when rx retry is enabled. The
 default value is 15.
 
 **--dequeue-zero-copy**
-Dequeue zero copy will be enabled when this option is given.
+Dequeue zero copy will be enabled when this option is given, it is worth to
+note that if NIC is binded to vfio-pci driver, dequeue zero copy cannot work 
+at VM2NIC mode (vm2vm=0) due to currently we don't setup iommu dma mapping for
+guest memory.
 
 **--vlan-strip 0|1**
 VLAN strip option is removed, because different NICs have different behaviors
-- 
2.0.1