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Subject: Re: [PATCH] usb/c67x00: Replace tasklet with work
To:     Davidlohr Bueso <dave@stgolabs.net>, jacmet@sunsite.dk
Cc:     gregkh@linuxfoundation.org, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>
References: <20210111044050.86763-1-dave@stgolabs.net>
From:   Sergei Shtylyov <sergei.shtylyov@gmail.com>
Organization: Brain-dead Software
Message-ID: <87dfaf4f-8a53-2840-c68c-fe10de1408e8@gmail.com>
Date:   Mon, 11 Jan 2021 11:37:47 +0300
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Hello!

On 11.01.2021 7:40, Davidlohr Bueso wrote:

> Tasklets have long been deprecated as being too heavy on the system
> by running in irq context - and this is not a performance critical
> path. If a higher priority process wants to run, it must wait for
> the tasklet to finish before doing so.
> 
> c67x00_do_work() will now run in process context and have further
> concurrency (tasklets being serialized among themselves), but this
> is done holding the c67x00->lock, so it should be fine. Furthermore,
> this patch fixes the usage of the lock in the callback as otherwise
> it would need to be irq-safe.
> 
> Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
[...]
> diff --git a/drivers/usb/c67x00/c67x00-sched.c b/drivers/usb/c67x00/c67x00-sched.c
> index e65f1a0ae80b..af60f4fdd340 100644
> --- a/drivers/usb/c67x00/c67x00-sched.c
> +++ b/drivers/usb/c67x00/c67x00-sched.c
> @@ -1123,24 +1123,26 @@ static void c67x00_do_work(struct c67x00_hcd *c67x00)
>   
>   /* -------------------------------------------------------------------------- */
>   
> -static void c67x00_sched_tasklet(struct tasklet_struct *t)
> +static void c67x00_sched_work(struct work_struct *work)
>   {
> -	struct c67x00_hcd *c67x00 = from_tasklet(c67x00, t, tasklet);
> +	struct c67x00_hcd *c67x00;
> +
> +	c67x00 = container_of(work, struct c67x00_hcd, work);
>   	c67x00_do_work(c67x00);
>   }
>   
>   void c67x00_sched_kick(struct c67x00_hcd *c67x00)
>   {
> -	tasklet_hi_schedule(&c67x00->tasklet);
> +        queue_work(system_highpri_wq, &c67x00->work);

     Use a tab to indent, please.

>   }
>   
>   int c67x00_sched_start_scheduler(struct c67x00_hcd *c67x00)
>   {
> -	tasklet_setup(&c67x00->tasklet, c67x00_sched_tasklet);
> +        INIT_WORK(&c67x00->work, c67x00_sched_work);

    Here as well.

>   	return 0;
>   }
>   
>   void c67x00_sched_stop_scheduler(struct c67x00_hcd *c67x00)
>   {
> -	tasklet_kill(&c67x00->tasklet);
> +        cancel_work_sync(&c67x00->work);

    And here.

[...]

MBR, Sergei