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Date:   Thu, 21 Jul 2022 09:50:23 -0400
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Weitao Wang <WeitaoWang-oc@zhaoxin.com>
Cc:     gregkh@linuxfoundation.org, kishon@ti.com, dianders@chromium.org,
        s.shtylyov@omp.ru, mka@chromium.org, ming.lei@canonical.com,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        tonywwang@zhaoxin.com, weitaowang@zhaoxin.com,
        CobeChen@zhaoxin.com, TimGuo@zhaoxin.com
Subject: Re: [PATCH] USB: HCD: Fix URB giveback issue in tasklet function
Message-ID: <YtlZn74MDEj+1On9@rowland.harvard.edu>
References: <20220721060833.4173-1-WeitaoWang-oc@zhaoxin.com>
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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