[spp] [PATCH 5/5] docs: add note regarding NUMA configuration

[x-fn-spp-ml at ntt-tx.co.jp]

From: Hideyuki Yamashita <yamashita.hideyuki at ntt-tx.co.jp>

This patch adds new notes for NUMA configuration when starting
spp_primary.

This is pointed out by the following DPDK Bugzilla tickets.
https://bugs.dpdk.org/show_bug.cgi?id=457

Signed-off-by: Hideyuki Yamashita <yamashita.hideyuki at ntt-tx.co.jp>
Signed-off-by: Naoki Takada <ntakada14 at gmail.com>
---
 docs/guides/gsg/howto_use.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/docs/guides/gsg/howto_use.rst b/docs/guides/gsg/howto_use.rst
index f182198..4f2e6cd 100644
--- a/docs/guides/gsg/howto_use.rst
+++ b/docs/guides/gsg/howto_use.rst
@@ -422,6 +422,18 @@ if you run the process on single NUMA node.
    If you use DPDK v18.11 or later, ``--base-virtaddr 0x100000000`` is enabled
    in default. You need to use this option only for changing the default value.
 
+.. note::
+
+   ``spp_primary`` tries to create memory pool in the same NUMA node where
+   it is launched. Under NUMA configuration, the NUMA node where ``spp_primary``
+   is launched and the NUMA node where NIC is connected can be different
+   (e.g. spp_primary runs in NUMA node 0 while NIC is connected with NUMA
+   node 1).
+   Such configuration may cause performance degradation. In general, under
+   NUMA configuration, it is best practice to use CPU and NIC which belongs
+   to the same NUMA node for best performance. So user should align those
+   when performance degradation makes the situation critical.
+
 If ``spp_primary`` is launched with two or more lcores, forwarder or monitor
 is activated. The default is forwarder and monitor is optional in this case.
 If you use monitor thread, additional option ``--disp-stat`` is required.
-- 
2.25.1