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

[Yasufumi Ogawa]

> 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.
> +
I have two comments.

1. Could I confirm WHAT should be configured for avoiding such a 
performance loss?

2. It seems something abruptly considering context of this section 
because you start talking about performance suddenly. If it must be 
considered as a mandatory configuration and should be explained this 
section, I agree your update. On the other hand, what do you think to 
move this note to the next "Performance Optimization" section. I think 
no need to be a note if you move it to the next secion.

Thanks

>   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.
>