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

[Sowjanya Komatineni]

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 ÐÐÑÐÑ:
> > > > > > > > > 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.

> > 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.