doc: add note for vhost builtin example

Add memory pre-allocation note for vhost example when enabling
"builtin-net-driver".

Signed-off-by: Xuan Ding <xuan.ding@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

diff --git a/doc/guides/sample_app_ug/vhost.rst b/doc/guides/sample_app_ug/vhost.rst
index a71ada6..b7ed4f8 100644 (file)
--- a/doc/guides/sample_app_ug/vhost.rst
+++ b/doc/guides/sample_app_ug/vhost.rst
@@ -201,3 +201,10 @@ Common Issues
 
   QEMU vhost net device start will fail if protocol feature is not negotiated.
   DPDK virtio-user pmd can be the replacement of QEMU.
+
+* Device start fails when enabling "builtin-net-driver" without memory
+  pre-allocation
+
+  The builtin example doesn't support dynamic memory allocation. When vhost
+  backend enables "builtin-net-driver", "--socket-mem" option should be
+  added at virtio-user pmd side as a startup item.