Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver

Sowjanya Komatineni
2020-04-06T22:07:57Z

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.
>
>
>