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

[WeitaoWang-oc@xxxxxxxxxxx]

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@xxxxxxxxxxx>
> > ---
> > 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
> .