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
