New upstream version 18.05

[deb_dpdk.git] / doc / guides / sample_app_ug / vhost.rst

diff --git a/doc/guides/sample_app_ug/vhost.rst b/doc/guides/sample_app_ug/vhost.rst
index a4bdc6a..9112e78 100644 (file)
--- 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
@@ -175,15 +178,17 @@ Common Issues
   The command above indicates how many hugepages are free to support QEMU's
   allocation request.
 
-* vhost-user will not work with QEMU without the ``-mem-prealloc`` option
+* Failed to build DPDK in VM
 
-  The current implementation works properly only when the guest memory is
-  pre-allocated.
+  Make sure "-cpu host" QEMU option is given.
 
-* vhost-user will not work with a QEMU version without shared memory mapping:
+* Device start fails if NIC's max queues > the default number of 128
 
-  Make sure ``share=on`` QEMU option is given.
+  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.
 
-* Failed to build DPDK in VM
+  Change the default number to make it work as below, just set the number
+  according to the NIC's property. ::
 
-  Make sure "-cpu host" QEMU option is given.
+      make EXTRA_CFLAGS="-DMAX_QUEUES=320"