Messages in this thread | | | Subject | Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver | From | Sowjanya Komatineni <> | Date | Tue, 7 Apr 2020 14:08:36 -0700 |
| |
On 4/6/20 4:48 PM, Sowjanya Komatineni wrote: > > 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
Just want to close on this part of feedback. Hope above explanation is clear regarding triggering/issuing at max 2 frame capture to VI HW and also regarding capture threads where they use wait_event_interruptible to prevent blocking waiting for buffers to be available for captures.
So no changes related to this part are needed in v7.
| |