X-Git-Url: http://git.droids-corp.org/?a=blobdiff_plain;f=doc%2Fguides%2Fsample_app_ug%2Fvhost.rst;h=9112e789706c57591aabcac5e374ff052d1ce303;hb=2808423a9ce42a748aed77a4b487be27d2b6acfa;hp=da161a9a91ae93d020761fa38f9cc94f95f58d89;hpb=768274ebbd5e532134420146cc26b1ff4b607740;p=dpdk.git

diff --git a/doc/guides/sample_app_ug/vhost.rst b/doc/guides/sample_app_ug/vhost.rst
index da161a9a91..9112e78970 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 driver with iommu enabled, 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
@@ -178,3 +181,14 @@ Common Issues
 * Failed to build DPDK in VM
 
   Make sure "-cpu host" QEMU option is given.
+
+* Device start fails if NIC's max queues > the default number of 128
+
+  mbuf pool size is dependent on the MAX_QUEUES configuration, if NIC's
+  max queue number is larger than 128, device start will fail due to
+  insufficient mbuf.
+
+  Change the default number to make it work as below, just set the number
+  according to the NIC's property. ::
+
+      make EXTRA_CFLAGS="-DMAX_QUEUES=320"