Re: [dpdk-dev] [PATCH v5 1/8] net/hns3: support runtime config to select IO burst func

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 3/19/2021 1:07 AM, Min Hu (Connor) wrote:
> From: Chengwen Feng <fengchengwen@huawei.com>
> 
> Currently, the driver support multiple IO burst function and auto
> selection of the most appropriate function based on offload
> configuration.
> 
> Most applications such as l2fwd/l3fwd don't provide the means to
> change offload configuration, so it will use the auto selection's io
> burst function.
> 
> This patch support runtime config to select io burst function, which
> add two config: rx_func_hint and tx_func_hint, both could assign
> vec/sve/simple/common.
> 
> The driver will use the following rules to select io burst func:
> a. if hint equal vec and meet the vec Rx/Tx usage condition then use
> the neon function.
> b. if hint equal sve and meet the sve Rx/Tx usage condition then use
> the sve function.
> c. if hint equal simple and meet the simple Rx/Tx usage condition then
> use the simple function.
> d. if hint equal common then use the common function.
> e. if hint not set then:
> e.1. if meet the vec Rx/Tx usage condition then use the neon function.
> e.2. if meet the simple Rx/Tx usage condition then use the simple
> function.
> e.3. else use the common function.
> 
> Note: the sve Rx/Tx usage condition based on the vec Rx/Tx usage
> condition and runtime environment (which must support SVE).
> 
> In the previous versions, driver will preferred use the sve function
> when meet the sve Rx/Tx usage condition, but in this case driver could
> get better performance if use the neon function.
> 

Is this saying 'neon' is giving better performance even if 'sve' is supported?

> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
> Signed-off-by: Min Hu (Connor) <humin29@huawei.com>
> ---
> v6:
> - document hns3.rst about description of vec, common and simple.
> ---
>   doc/guides/nics/hns3.rst               | 19 +++++++++
>   doc/guides/rel_notes/release_21_05.rst |  1 +
>   drivers/net/hns3/hns3_ethdev.c         | 77 ++++++++++++++++++++++++++++++++++
>   drivers/net/hns3/hns3_ethdev.h         | 15 +++++++
>   drivers/net/hns3/hns3_ethdev_vf.c      |  4 ++
>   drivers/net/hns3/hns3_rxtx.c           | 54 +++++++++++++++++-------
>   6 files changed, 156 insertions(+), 14 deletions(-)
> 
> diff --git a/doc/guides/nics/hns3.rst b/doc/guides/nics/hns3.rst
> index 84bd7a3..8f48240 100644
> --- a/doc/guides/nics/hns3.rst
> +++ b/doc/guides/nics/hns3.rst
> @@ -46,6 +46,25 @@ Prerequisites
>   - Follow the DPDK :ref:`Getting Started Guide for Linux <linux_gsg>` to setup the basic DPDK environment.
>   
>   
> +Runtime Config Options
> +----------------------
> +
> +- ``rx_func_hint`` (default ``none``)
> +
> +  Used to select Rx burst function, supported value are "vec", "sve", "simple", "common".

``vec``, ``sve``, ``simple`` and ``common``. ??

> +  When equal "vec" and meet the vector Rx usage condition then use the default vector Rx implementation, 'neon' for Kunpeng Arm platform.
> +  When equal "sve" and meet the sve Rx usage condition then use the sve Rx function.
> +  When equal "simple" and meet the simple Rx usage condition then use the simple Rx function which indicates the Scalar algorithm obtained from rte_eth_rx_burst_mode_get.
> +  When equal "common" then use the common Rx function which indicates the Scalar Scattered algorithm obtained from rte_eth_rx_burst_mode_get.
> +

A few comments on the documentation,

- What about using `` to highlight the parameter, like ``vec``, on all occurrences.

- What about adding bullet points for each parameter

- I think you can drop "When equal" start from all

- You can drop "obtained from rte_eth_rx_burst_mode_get" part, the function name 
is not needed here, something like gives same information:

- Can "and meet the vector Rx usage condition" be simplified, overall what about 
something like:
* ``simple``, if supported use the ``simple`` Rx function which indicates the 
scalar algorithm.

- It is not clear what happens when provided parameter is not supported, like 
when I set 'vec' but if PMD doesn't support it, which function will be supported?

- Can you please try to limit the line length aroung 80 columns.

- No need to start words with uppercase for 'Scalar' & 'Scalar Scattered'

- Same for below Tx ones.