Messages in this thread | | | Subject | Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver | From | Sowjanya Komatineni <> | Date | Mon, 6 Apr 2020 16:48:41 -0700 |
| |
On 4/6/20 4:18 PM, Dmitry Osipenko wrote: > External email: Use caution opening links or attachments > > > 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. we hold on to issuing capture if more than 2 buffers are queued and it continues only after fifo has min 1 slot empty
| |