linux-kernel - Re: [PATCH] Add Multiple TX/RX Queues Support for WWAN Network Device

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Date:   Wed, 8 Dec 2021 17:53:31 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     <xiayu.zhang@...iatek.com>
Cc:     <loic.poulain@...aro.org>, <ryazanov.s.a@...il.com>,
        <davem@...emloft.net>, <johannes@...solutions.net>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <haijun.liu@...iatek.com>, <zhaoping.shu@...iatek.com>,
        <hw.he@...iatek.com>, <srv_heupstream@...iatek.com>
Subject: Re: [PATCH] Add Multiple TX/RX Queues Support for WWAN Network
 Device

On Wed, 8 Dec 2021 12:04:14 +0800 xiayu.zhang@...iatek.com wrote:
> From: Xiayu Zhang <Xiayu.Zhang@...iatek.com>
> 
> This patch adds 2 callback functions get_num_tx_queues() and
> get_num_rx_queues() to let WWAN network device driver customize its own
> TX and RX queue numbers. It gives WWAN driver a chance to implement its
> own software strategies, such as TX Qos.
> 
> Currently, if WWAN device driver creates default bearer interface when
> calling wwan_register_ops(), there will be only 1 TX queue and 1 RX queue
> for the WWAN network device. In this case, driver is not able to enlarge
> the queue numbers by calling netif_set_real_num_tx_queues() or
> netif_set_real_num_rx_queues() to take advantage of the network device's
> capability of supporting multiple TX/RX queues.
> 
> As for additional interfaces of secondary bearers, if userspace service
> doesn't specify the num_tx_queues or num_rx_queues in netlink message or
> iproute2 command, there also will be only 1 TX queue and 1 RX queue for
> each additional interface. If userspace service specifies the num_tx_queues
> and num_rx_queues, however, these numbers could be not able to match the
> capabilities of network device.
> 
> Besides, userspace service is hard to learn every WWAN network device's
> TX/RX queue numbers.
> 
> In order to let WWAN driver determine the queue numbers, this patch adds
> below callback functions in wwan_ops:
>     struct wwan_ops {
>         unsigned int priv_size;
>         ...
>         unsigned int (*get_num_tx_queues)(unsigned int hint_num);
>         unsigned int (*get_num_rx_queues)(unsigned int hint_num);
>     };
> 
> WWAN subsystem uses the input parameters num_tx_queues and num_rx_queues of
> wwan_rtnl_alloc() as hint values, and passes the 2 values to the two
> callback functions. WWAN device driver should determine the actual numbers
> of network device's TX and RX queues according to the hint value and
> device's capabilities.

I'll mark it as an RFC in patchwork, there needs to be an in-tree user
for this code to be merged.