hi Ming:
>>> One approach I like to use is trace event.
>> Would you please let us how to to use trace event for calculate
>> max/average usb irq time?
>
> You can enable irq_handler_entry and irq_handler_exit event, then
> write a script easily to figure out the time consumed in ehci irq handler,
> see Documentation/trace/events.txt of linux kernel for detailed steps.
I find it ^^
>>> But actually the local interrupt is still disabled during completion
>>> because we need to convert spin_lock in all current usb drivers
>>> to spin_lock_irqsave() first.
>> Would you please let me know the function or source you mentioned?
>
> The local interrupt is disabled during completion handler in
> __usb_hcd_giveback_urb().
>
>>
>> BTW, why I cannot see xhci add HCD_BH?
>
> There might be some reasons:
>
> - in previous following up discussion, Alan thought it should
> be easier to just split the hcd interrupt handler into two parts
>
> - as I said, spin_lock() isn't converted to spin_lock_irqsave()
> in drivers' completion handler yet
Do you mean ,
take uvc/uac for example,
if we put completion what they register previously in BH,
the spin_lock() in their completions should be changed to spin_lock_irqsave()?
Is it due to original completion is called in irq context?
>
> - maybe no one really care the time in which local interrupt is
> disabled by USB completion handler.(That might be true
> because USB devices are commonly used in personal
> computer, not in big server product)
>
>> is there some reason xhci cannot put completion in BH?
>
> IMO, the completion handler should be put into tasklet, and
> can be done. If you like, you can take time to do that.
Below is so far kernel implementation.
Isn't it put completion handler into tasklet?
.......................
......................
spin_lock(&bh->lock);
list_add_tail(&urb->urb_list, &bh->head);
running = bh->running;
spin_unlock(&bh->lock);
if (running)
;
else if (high_prio_bh)
tasklet_hi_schedule(&bh->bh);
else
tasklet_schedule(&bh->bh);
Thanks for your help,
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