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References: <20240227172852.2386358-1-tj@kernel.org> <20240227172852.2386358-7-tj@kernel.org>
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From: Allen <allen.lkml@gmail.com>
Date: Wed, 28 Feb 2024 09:33:40 -0800
Message-ID: <CAOMdWSLVDaN_XFD6Ov-=6VrH4wyBz-0wq_L3EzgdsJ5zJi47qQ@mail.gmail.com>
Subject: Re: [PATCH 6/6] r8152: Convert from tasklet to BH workqueue
To: Tejun Heo <tj@kernel.org>
Cc: jiangshanlai@gmail.com, torvalds@linux-foundation.org, 
	linux-kernel@vger.kernel.org, kernel-team@meta.com, boqun.feng@gmail.com, 
	tglx@linutronix.de, peterz@infradead.org, romain.perier@gmail.com, 
	mingo@kernel.org
Content-Type: text/plain; charset="UTF-8"

> tasklet is being replaced by BH workqueue. No noticeable behavior or
> performance changes are expected. The following is how the two APIs map:
>
> - tasklet_setup/init()          -> INIT_WORK()
> - tasklet_schedule()            -> queue_work(system_bh_wq, ...)
> - tasklet_hi_schedule()         -> queue_work(system_bh_highpri_wq, ...)
> - tasklet_disable_nosync()      -> disable_work()
> - tasklet_disable[_in_atomic]() -> disable_work_sync()
> - tasklet_enable()              -> enable_work() + queue_work()
> - tasklet_kill()                -> cancel_work_sync()
>
> Note that unlike tasklet_enable(), enable_work() doesn't queue the work item
> automatically according to whether the work item was queued while disabled.
> While the caller can track this separately, unconditionally scheduling the
> work item after enable_work() returns %true should work for most users.
>
> r8152 conversion has been tested by repeatedly forcing the device to go
> through resets using usbreset under iperf3 generated traffic.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> ---
>  drivers/net/usb/r8152.c | 44 ++++++++++++++++++++++-------------------
>  1 file changed, 24 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
> index 9bf2140fd0a1..24e284b9eb38 100644
> --- a/drivers/net/usb/r8152.c
> +++ b/drivers/net/usb/r8152.c
> @@ -882,7 +882,7 @@ struct r8152 {
>  #ifdef CONFIG_PM_SLEEP
>         struct notifier_block pm_notifier;
>  #endif
> -       struct tasklet_struct tx_tl;
> +       struct work_struct tx_work;
>
>         struct rtl_ops {
>                 void (*init)(struct r8152 *tp);
> @@ -1948,7 +1948,7 @@ static void write_bulk_callback(struct urb *urb)
>                 return;
>
>         if (!skb_queue_empty(&tp->tx_queue))
> -               tasklet_schedule(&tp->tx_tl);
> +               queue_work(system_bh_wq, &tp->tx_work);
>  }
>
>  static void intr_callback(struct urb *urb)
> @@ -2746,9 +2746,9 @@ static void tx_bottom(struct r8152 *tp)
>         } while (res == 0);
>  }
>
> -static void bottom_half(struct tasklet_struct *t)
> +static void bottom_half(struct work_struct *work)
>  {
> -       struct r8152 *tp = from_tasklet(tp, t, tx_tl);
> +       struct r8152 *tp = container_of(work, struct r8152, tx_work);
>
>         if (test_bit(RTL8152_INACCESSIBLE, &tp->flags))
>                 return;
> @@ -2942,7 +2942,7 @@ static netdev_tx_t rtl8152_start_xmit(struct sk_buff *skb,
>                         schedule_delayed_work(&tp->schedule, 0);
>                 } else {
>                         usb_mark_last_busy(tp->udev);
> -                       tasklet_schedule(&tp->tx_tl);
> +                       queue_work(system_bh_wq, &tp->tx_work);
>                 }
>         } else if (skb_queue_len(&tp->tx_queue) > tp->tx_qlen) {
>                 netif_stop_queue(netdev);
> @@ -6824,11 +6824,12 @@ static void set_carrier(struct r8152 *tp)
>         } else {
>                 if (netif_carrier_ok(netdev)) {
>                         netif_carrier_off(netdev);
> -                       tasklet_disable(&tp->tx_tl);
> +                       disable_work_sync(&tp->tx_work);
>                         napi_disable(napi);
>                         tp->rtl_ops.disable(tp);
>                         napi_enable(napi);
> -                       tasklet_enable(&tp->tx_tl);
> +                       enable_work(&tp->tx_work);
> +                       queue_work(system_bh_wq, &tp->tx_work);
>                         netif_info(tp, link, netdev, "carrier off\n");
>                 }
>         }
> @@ -6864,7 +6865,7 @@ static void rtl_work_func_t(struct work_struct *work)
>         /* don't schedule tasket before linking */
>         if (test_and_clear_bit(SCHEDULE_TASKLET, &tp->flags) &&
>             netif_carrier_ok(tp->netdev))
> -               tasklet_schedule(&tp->tx_tl);
> +               queue_work(system_bh_wq, &tp->tx_work);
>
>         if (test_and_clear_bit(RX_EPROTO, &tp->flags) &&
>             !list_empty(&tp->rx_done))
> @@ -6971,7 +6972,7 @@ static int rtl8152_open(struct net_device *netdev)
>                 goto out_unlock;
>         }
>         napi_enable(&tp->napi);
> -       tasklet_enable(&tp->tx_tl);
> +       enable_work(&tp->tx_work);

  I think we are missing queue_work() above, right?

   To avoid such situations, could we combine enable_work() + queue_work(),
into a single API?
Perhaps, something like:

static inline bool enable_and_queue_work(struct workqueue_struct *wq,
struct work_struct *work)
{
       if (enable_work(work))
       {
             queue_work(wq, work);
             return true;
       }
       return false;
}


Thanks,
Allen


>         mutex_unlock(&tp->control);
>
> @@ -6999,7 +7000,7 @@ static int rtl8152_close(struct net_device *netdev)
>  #ifdef CONFIG_PM_SLEEP
>         unregister_pm_notifier(&tp->pm_notifier);
>  #endif
> -       tasklet_disable(&tp->tx_tl);
> +       disable_work_sync(&tp->tx_work);
>         clear_bit(WORK_ENABLE, &tp->flags);
>         usb_kill_urb(tp->intr_urb);
>         cancel_delayed_work_sync(&tp->schedule);
> @@ -8421,7 +8422,7 @@ static int rtl8152_pre_reset(struct usb_interface *intf)
>                 return 0;
>
>         netif_stop_queue(netdev);
> -       tasklet_disable(&tp->tx_tl);
> +       disable_work_sync(&tp->tx_work);
>         clear_bit(WORK_ENABLE, &tp->flags);
>         usb_kill_urb(tp->intr_urb);
>         cancel_delayed_work_sync(&tp->schedule);
> @@ -8466,7 +8467,8 @@ static int rtl8152_post_reset(struct usb_interface *intf)
>         }
>
>         napi_enable(&tp->napi);
> -       tasklet_enable(&tp->tx_tl);
> +       enable_work(&tp->tx_work);
> +       queue_work(system_bh_wq, &tp->tx_work);
>         netif_wake_queue(netdev);
>         usb_submit_urb(tp->intr_urb, GFP_KERNEL);
>
> @@ -8625,12 +8627,13 @@ static int rtl8152_system_suspend(struct r8152 *tp)
>
>                 clear_bit(WORK_ENABLE, &tp->flags);
>                 usb_kill_urb(tp->intr_urb);
> -               tasklet_disable(&tp->tx_tl);
> +               disable_work_sync(&tp->tx_work);
>                 napi_disable(napi);
>                 cancel_delayed_work_sync(&tp->schedule);
>                 tp->rtl_ops.down(tp);
>                 napi_enable(napi);
> -               tasklet_enable(&tp->tx_tl);
> +               enable_work(&tp->tx_work);
> +               queue_work(system_bh_wq, &tp->tx_work);
>         }
>
>         return 0;
> @@ -9387,11 +9390,12 @@ static int rtl8152_change_mtu(struct net_device *dev, int new_mtu)
>                 if (netif_carrier_ok(dev)) {
>                         netif_stop_queue(dev);
>                         napi_disable(&tp->napi);
> -                       tasklet_disable(&tp->tx_tl);
> +                       disable_work_sync(&tp->tx_work);
>                         tp->rtl_ops.disable(tp);
>                         tp->rtl_ops.enable(tp);
>                         rtl_start_rx(tp);
> -                       tasklet_enable(&tp->tx_tl);
> +                       enable_work(&tp->tx_work);
> +                       queue_work(system_bh_wq, &tp->tx_work);
>                         napi_enable(&tp->napi);
>                         rtl8152_set_rx_mode(dev);
>                         netif_wake_queue(dev);
> @@ -9819,8 +9823,8 @@ static int rtl8152_probe_once(struct usb_interface *intf,
>         mutex_init(&tp->control);
>         INIT_DELAYED_WORK(&tp->schedule, rtl_work_func_t);
>         INIT_DELAYED_WORK(&tp->hw_phy_work, rtl_hw_phy_work_func_t);
> -       tasklet_setup(&tp->tx_tl, bottom_half);
> -       tasklet_disable(&tp->tx_tl);
> +       INIT_WORK(&tp->tx_work, bottom_half);
> +       disable_work(&tp->tx_work);
>
>         netdev->netdev_ops = &rtl8152_netdev_ops;
>         netdev->watchdog_timeo = RTL8152_TX_TIMEOUT;
> @@ -9954,7 +9958,7 @@ static int rtl8152_probe_once(struct usb_interface *intf,
>         unregister_netdev(netdev);
>
>  out1:
> -       tasklet_kill(&tp->tx_tl);
> +       cancel_work_sync(&tp->tx_work);
>         cancel_delayed_work_sync(&tp->hw_phy_work);
>         if (tp->rtl_ops.unload)
>                 tp->rtl_ops.unload(tp);
> @@ -10010,7 +10014,7 @@ static void rtl8152_disconnect(struct usb_interface *intf)
>                 rtl_set_unplug(tp);
>
>                 unregister_netdev(tp->netdev);
> -               tasklet_kill(&tp->tx_tl);
> +               cancel_work_sync(&tp->tx_work);
>                 cancel_delayed_work_sync(&tp->hw_phy_work);
>                 if (tp->rtl_ops.unload)
>                         tp->rtl_ops.unload(tp);
> --
> 2.43.2
>


-- 
       - Allen