linux-kernel - Re: [PATCH v2] USB: HCD: Fix URB giveback issue in tasklet function

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Date:   Mon, 25 Jul 2022 11:29:33 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...il.com>
To:     Weitao Wang <WeitaoWang-oc@...oxin.com>, stern@...land.harvard.edu,
        gregkh@...uxfoundation.org, kishon@...com, dianders@...omium.org,
        s.shtylyov@....ru, mka@...omium.org, ming.lei@...onical.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     tonywwang@...oxin.com, weitaowang@...oxin.com
Subject: Re: [PATCH v2] USB: HCD: Fix URB giveback issue in tasklet function

Hello!

On 7/25/22 9:52 AM, Weitao Wang wrote:

> Usb core introduce the mechanism of giveback of URB in tasklet context to
> reduce hardware interrupt handling time. On some test situation(such as
> FIO with 4KB block size), when tasklet callback function called to
> giveback URB, interrupt handler add URB node to the bh->head list also.
> If check bh->head list again after finish all URB giveback of local_list,
> then it may introduce a "dynamic balance" between giveback URB and add URB
> to bh->head list. This tasklet callback function may not exit for a long
> time, which will cause other tasklet function calls to be delayed. Some
> real-time applications(such as KB and Mouse) will see noticeable lag.
> 
> Fix this issue by taking new URBs giveback in next tasklet function call.
> Add a member high_prio for structure giveback_urb_bh and replace the local
> high_prio_bh variable with this structure member in usb_hcd_giveback_urb.
> 
> Fixes: 94dfd7edfd5c ("USB: HCD: support giveback of URB in tasklet context")
> Signed-off-by: Weitao Wang <WeitaoWang-oc@...oxin.com>
> ---
> v1->v2:
>  - Fix compile warning by remove label "restart".
>  - Modify the patch description info.
>  - Change structure member from hi_priority to high_prio.
> 
>  drivers/usb/core/hcd.c  | 25 ++++++++++++++-----------
>  include/linux/usb/hcd.h |  1 +
>  2 files changed, 15 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index 06eea8848ccc..1feb9a604380 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
[...]
> @@ -2959,6 +2961,7 @@ int usb_add_hcd(struct usb_hcd *hcd,
>  
>  	/* initialize tasklets */
>  	init_giveback_urb_bh(&hcd->high_prio_bh);
> +	hcd->high_prio_bh.high_prio = 1;

   s/1/true/?

>  	init_giveback_urb_bh(&hcd->low_prio_bh);
>  
>  	/* enable irqs just before we start the controller,
> diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
> index 2c1fc9212cf2..98d1921f02b1 100644
> --- a/include/linux/usb/hcd.h
> +++ b/include/linux/usb/hcd.h
> @@ -66,6 +66,7 @@
>  
>  struct giveback_urb_bh {
>  	bool running;
> +	bool high_prio;
>  	spinlock_t lock;
>  	struct list_head  head;
>  	struct tasklet_struct bh;

MBR, Sergey