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

[WeitaoWang-oc@xxxxxxxxxxx]

On 2022/7/25 21:58, Alan Stern wrote:
> On Mon, Jul 25, 2022 at 02:52:51PM +0800, Weitao Wang wrote:
>
> This is basically okay.  Just a couple of small comments...
>
> > 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.
>
> The patch description should do more than say what the new code _is_ --
> we can see that easily enough by reading the patch.  The description
> should explain _why_ the code was changed.
Okay, I will improve this patch description.

> > -	/* check if there are new URBs to giveback */
> > +	/* giveback new URBs next time to prevent this function from
> > +	 * not exiting for a long time.
> > +	 */
>
> Minor stylistic issue: The currently accepted format for multi-line
> comments is like this:
This notes will be improved in next patch version also.
Thanks for your suggestion.

weitao
> 	/*
> 	 * Blah blah blah
> 	 * Blah blah blah
> 	 */
>
> Alan Stern
> .