Message-ID: <6f4ae1d8b1b53cf998eaa14260d93fd3f4c8d5ad.camel@mediatek.com>
Date:   Mon, 13 Dec 2021 14:06:31 +0800
From:   Xiayu Zhang <xiayu.zhang@...iatek.com>
To:     Sergey Ryazanov <ryazanov.s.a@...il.com>
CC:     Loic Poulain <loic.poulain@...aro.org>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Johannes Berg <johannes@...solutions.net>,
        <netdev@...r.kernel.org>, open list <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

Hi Sergey,

Thanks for your constructive inputs, and sorry for late response.

Indeed, I had considered this solution provided by you as well:

   static unsigned int wwan_rtnl_get_num_tx_queues(struct nlattr *tb[])

   static struct rtnl_link_ops wwan_rtnl_link_ops __read_mostly = {
      ...
      .get_num_tx_queues = wwan_rtnl_get_num_tx_queues,
   };

I totally agree that it follows the design of RTNL better.

There are some reasons that let me not apply the solution above, I want
to share them with you. Please correct me if I'm wrong.

   1) in rtnl_create_link, RTNL always prefers to use the number
   provided by userspace service rather than the number returned by
   get_num_tx/rx_queues() of WWAN Core:

      if (tb[IFLA_NUM_TX_QUEUES])
         num_tx_queues = nla_get_u32(tb[IFLA_NUM_TX_QUEUES]);
      else if (ops->get_num_tx_queues)
         num_tx_queues = ops->get_num_tx_queues();

   Although WWAN driver could reject the number selected by userspace
   service in newlink function, this will require userspace service to
   learn this error and implement its retry machanisms. Of course, even
   so, that's not bad.

   I think it's probably better to let WWAN device driver determine
   its default queue number.

   2) As you described, above solution will modify the definition and
   usage of get_num_tx_queues() and get_num_rx_queues() in
   rtnl_link_ops. Userspace service also needs to add new NETLINK
   attributes.

   3) WWAN subsystem implements the rtnl_link_ops and plays a role of
   the bridge between RTNL and WWAN device driver. As a separate
   subsystem, I think it could be able to supply its own callback
   functions to WWAN device driver in wwan_ops just as shown in this
   patch.

   In addition to these reasons, I also agree with your points:
      "can be assumed too intrusive to implement a one feature for 
      a single subsystem."

Please review my thoughts and give me some inputs at your convenience.


On Fri, 2021-12-10 at 02:11 +0300, Sergey Ryazanov wrote:
> On Wed, Dec 8, 2021 at 7:04 AM <xiayu.zhang@...iatek.com> wrote:
> > 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.
> 
> As already stated by Jakub, it is hard to understand a new API
> suitability without an API user. I will try to describe possible
> issues with the proposed API as far as I understand its usage and
> possible solutions. Correct me if I am wrong.
> 
> There are actually two tasks related to the queues number selection:
> 1) default queues number selection if the userspace provides no
> information about a wishful number of queues;
> 2) rejecting the new netdev (bearer) creation if a requested number
> of
> queues seems to be invalid.
> 
> Your proposal tries to solve both of these tasks with a single hook
> that silently increases or decreases the requested number of queues.
> This is creative, but seems contradictory to regular RTNL behavior.
> RTNL usually selects a correct default value if no value was
> requested, or performs what is requested, or explicitly rejects
> requested configuration.
> 
> You could handle an invalid queues configuration in the .newlink
> callback. This callback is even able to return a string error
> representation via the extack argument.
> 
> As for the default queues number selection it seems better to
> implement the RTNL .get_num_rx_queues callback in the WWAN core and
> call optional driver specific callback through it. Something like
> this:
> 
> static unsigned int wwan_rtnl_get_num_tx_queues(struct nlattr *tb[])
> {
>     const char *devname = nla_data(tb[IFLA_PARENT_DEV_NAME]);
>     struct wwan_device *wwandev = wwan_dev_get_by_name(devname);
> 
>     return wwandev && wwandev->ops && wwandev->ops->get_num_tx_queues 
> ?
>               wwandev->ops->get_num_tx_queues() : 1;
> }
> 
> static struct rtnl_link_ops wwan_rtnl_link_ops __read_mostly = {
>     ...
>     .get_num_tx_queues = wwan_rtnl_get_num_tx_queues,
> };
> 
> This way the default queues number selection will be implemented in a
> less surprising way.
> 
> But to be able to implement this we need to modify the RTNL ops
> .get_num_tx_queues/.get_num_rx_queues callback definitions to make
> them able to accept the RTM_NEWLINK message attributes. This is not
> difficult since the callbacks are implemented only by a few virtual
> devices, but can be assumed too intrusive to implement a one feature
> for a single subsystem.
> 
> > Signed-off-by: Xiayu Zhang <Xiayu.Zhang@...iatek.com>
> > ---
> >  drivers/net/wwan/wwan_core.c | 25 ++++++++++++++++++++++++-
> >  include/linux/wwan.h         |  6 ++++++
> >  2 files changed, 30 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/wwan/wwan_core.c
> > b/drivers/net/wwan/wwan_core.c
> > index d293ab688044..00095c6987be 100644
> > --- a/drivers/net/wwan/wwan_core.c
> > +++ b/drivers/net/wwan/wwan_core.c
> > @@ -823,6 +823,7 @@ static struct net_device
> > *wwan_rtnl_alloc(struct nlattr *tb[],
> >         struct wwan_device *wwandev =
> > wwan_dev_get_by_name(devname);
> >         struct net_device *dev;
> >         unsigned int priv_size;
> > +       unsigned int num_txqs, num_rxqs;
> > 
> >         if (IS_ERR(wwandev))
> >                 return ERR_CAST(wwandev);
> > @@ -833,9 +834,31 @@ static struct net_device
> > *wwan_rtnl_alloc(struct nlattr *tb[],
> >                 goto out;
> >         }
> > 
> > +       /* let wwan device driver determine TX queue number if it
> > wants */
> > +       if (wwandev->ops->get_num_tx_queues) {
> > +               num_txqs = wwandev->ops-
> > >get_num_tx_queues(num_tx_queues);
> > +               if (num_txqs < 1 || num_txqs > 4096) {
> > +                       dev = ERR_PTR(-EINVAL);
> > +                       goto out;
> > +               }
> > +       } else {
> > +               num_txqs = num_tx_queues;
> > +       }
> > +
> > +       /* let wwan device driver determine RX queue number if it
> > wants */
> > +       if (wwandev->ops->get_num_rx_queues) {
> > +               num_rxqs = wwandev->ops-
> > >get_num_rx_queues(num_rx_queues);
> > +               if (num_rxqs < 1 || num_rxqs > 4096) {
> > +                       dev = ERR_PTR(-EINVAL);
> > +                       goto out;
> > +               }
> > +       } else {
> > +               num_rxqs = num_rx_queues;
> > +       }
> > +
> >         priv_size = sizeof(struct wwan_netdev_priv) + wwandev->ops-
> > >priv_size;
> >         dev = alloc_netdev_mqs(priv_size, ifname, name_assign_type,
> > -                              wwandev->ops->setup, num_tx_queues,
> > num_rx_queues);
> > +                              wwandev->ops->setup, num_txqs,
> > num_rxqs);
> > 
> >         if (dev) {
> >                 SET_NETDEV_DEV(dev, &wwandev->dev);
> > diff --git a/include/linux/wwan.h b/include/linux/wwan.h
> > index 9fac819f92e3..69c0af7ab6af 100644
> > --- a/include/linux/wwan.h
> > +++ b/include/linux/wwan.h
> > @@ -156,6 +156,10 @@ static inline void *wwan_netdev_drvpriv(struct
> > net_device *dev)
> >   * @setup: set up a new netdev
> >   * @newlink: register the new netdev
> >   * @dellink: remove the given netdev
> > + * @get_num_tx_queues: determine number of transmit queues
> > + *                     to create when creating a new device.
> > + * @get_num_rx_queues: determine number of receive queues
> > + *                     to create when creating a new device.
> >   */
> >  struct wwan_ops {
> >         unsigned int priv_size;
> > @@ -164,6 +168,8 @@ struct wwan_ops {
> >                        u32 if_id, struct netlink_ext_ack *extack);
> >         void (*dellink)(void *ctxt, struct net_device *dev,
> >                         struct list_head *head);
> > +       unsigned int (*get_num_tx_queues)(unsigned int hint_num);
> > +       unsigned int (*get_num_rx_queues)(unsigned int hint_num);
> >  };
> > 
> >  int wwan_register_ops(struct device *parent, const struct wwan_ops
> > *ops,
> 
> 

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