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

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Date:   Mon, 25 Jul 2022 16:52:17 +0800
From:   "WeitaoWang-oc@...oxin.com" <WeitaoWang-oc@...oxin.com>
To:     Sergei Shtylyov <sergei.shtylyov@...il.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

On 2022/7/25 16:29, Sergei Shtylyov wrote:
> 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/?
Okay,this Boolean variable should be initialized to ture.
Thanks for your suggestion.

weitao
>>   	init_giveback_urb_bh(&k->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
> .