doc: add note for maximum queues setting in vhost sample

If the NIC has a queue number larger than 128, then we need to change
the ``MAX_QUEUES`` to a larger number to make sure we allocate a big
enough memory pool for device setup.

Signed-off-by: Xiao Wang <xiao.w.wang@intel.com>
Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Marko Kovacevic <marko.kovacevic@intel.com>

diff --git a/doc/guides/sample_app_ug/vhost.rst b/doc/guides/sample_app_ug/vhost.rst
index 5e7f24c4e8bd75f940b176c1aba655c3825d78d2..9112e789706c57591aabcac5e374ff052d1ce303 100644 (file)
--- a/doc/guides/sample_app_ug/vhost.rst
+++ b/doc/guides/sample_app_ug/vhost.rst
@@ -181,3 +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"