Messages in this thread | | | Date | Thu, 21 Jul 2022 16:52:11 +0800 | Subject | Re: [PATCH] USB: HCD: Fix URB giveback issue in tasklet function | From | "" <> |
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On 2022/7/21 16:00, Oliver Neukum wrote: > > > On 21.07.22 08:08, 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. >> > > Hi, > > ow do you know usb_hcd_giveback_urb() will be called in time to process > isoc URBs in time, if you leave them on the list? In fact how do > you be sure it will be called at all? I can see no upper time limit > on that. > > Regards > Oliver > > . If the bh->head list is not empty, patch method will raise a softirq immediately to call work function of every tasklet. Therefore, I think the left URB in bh->head list will be get giveback in time.
Thanks weitao
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