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

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Message-ID: <d9ce5dbb-0ca0-b2b3-ad8d-9fbf0c2ed39e@zhaoxin.com>
Date:   Fri, 22 Jul 2022 10:31:24 +0800
From:   "WeitaoWang-oc@...oxin.com" <WeitaoWang-oc@...oxin.com>
To:     Alan Stern <stern@...land.harvard.edu>
CC:     <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>, <tonywwang@...oxin.com>,
        <weitaowang@...oxin.com>, <CobeChen@...oxin.com>,
        <TimGuo@...oxin.com>
Subject: Re: [PATCH] USB: HCD: Fix URB giveback issue in tasklet function

On 2022/7/21 21:50, Alan Stern wrote:
> On Thu, Jul 21, 2022 at 02:08:33PM +0800, 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.
> 
> The patch also replaces the local high_prio_bh variable with a new
> bh->high_prio structure member.  This should be mentioned in the patch
> description.
> 
> Alan Stern
> .
Okay,I will take your suggestion and submit a revised version.

Thanks
weitao