07.04.2020 01:07, Sowjanya Komatineni пишет: > > On 4/6/20 3:00 PM, Sowjanya Komatineni wrote: >> >> On 4/6/20 2:39 PM, Sowjanya Komatineni wrote: >>> >>> On 4/6/20 2:15 PM, Sowjanya Komatineni wrote: >>>> >>>> On 4/6/20 2:11 PM, Dmitry Osipenko wrote: >>>>> External email: Use caution opening links or attachments >>>>> >>>>> >>>>> 07.04.2020 00:02, Sowjanya Komatineni пишет: >>>>>>>>>>> Am I understanding correctly that this thread will take 100% >>>>>>>>>>> CPU, >>>>>>>>>>> spinning here, if more than 2 frame-captures queued? >>>>>>>>>> on more than 2 frames captures, it breaks thread and on next >>>>>>>>>> wakeup it >>>>>>>>>> continues >>>>>>>>> The wait_event() won't wait if condition is true. >>>>>>>> condition is checked when waitqueue is woken up >>>>>>> https://elixir.bootlin.com/linux/v5.6.2/source/include/linux/wait.h#L462 >>>>>>> >>>>>> process is put to sleep until the condition evaluates to true or >>>>>> signal >>>>>> is received. >>>>>> >>>>>> condition is checked each time the waitqueue head is woken up. >>>>> This is a wrong assumption in accordance to the code. >> >> process is in sleep until the condition is evaluated and when >> condition is true wakeup still happens only when wake_up on waitqueue >> is called >> >> This is the reason for using this to prevent blocking while waiting >> for the buffers. > > w.r.t capture list update, wakeup happens when wake_up on waitqueue is > called. > > wakeup also happens on kthread stop signal event. > >> >> >>>> >>>> when every buffer is available as long as we are in streaming, we >>>> should process it. >>>> >>>> So if wake up happens when list has buffer, it will be processed but >>>> at a time we limit processing 2 simultaneous buffer capture starts >>>> only. >>>> >>> Fixing typo. >>> >>> I meant when ever buffer is available as long as we are in streaming, >>> we should process it. >>> >>> So capture thread processes as long as buffers are available from >>> user space limiting 2 simultaneous trigger of captures and thread >>> will be in sleep when capture buffers list is empty or no stop thread >>> is signaled. IIUC, the waiting won't happen if more than 2 captures are queued and thread will be spinning until captures are processed. I think you need a semaphore with resource count = 2.
