From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sowjanya Komatineni Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver Date: Mon, 6 Apr 2020 16:48:41 -0700 Message-ID: <97b35910-4c93-123a-43a0-eb14476ed0f3@nvidia.com> References: <1585963507-12610-1-git-send-email-skomatineni@nvidia.com> <1585963507-12610-7-git-send-email-skomatineni@nvidia.com> <200bb96e-2d07-764f-9e14-55538dc742fd@gmail.com> <23bfab09-b464-6e51-9843-06d13000e9b9@nvidia.com> <08cd31d5-e8b9-4d3a-fb0e-0e4462947d96@nvidia.com> <12a834ac-52b1-6dc0-7d3a-3e6a1fa85a2a@gmail.com> <760d071e-0cbc-b3eb-9231-fb9f9ecb44a6@nvidia.com> <9e317f65-8a02-3b15-cfec-8e0d8374130e@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <9e317f65-8a02-3b15-cfec-8e0d8374130e-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Content-Language: en-US Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Dmitry Osipenko , thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, frankc-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, hverkuil-qWit8jRvyhVmR6Xm/wNWPw@public.gmane.org, sakari.ailus-X3B1VOXEql0@public.gmane.org, helen.koike-ZGY8ohtN/8qB+jHODAdFcQ@public.gmane.org Cc: sboyd-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, linux-media-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-clk-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-tegra@vger.kernel.org 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 =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> 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 =D0=BF=D0=B8=D1=88=D0=B5=D1=82= : >>>>>>>>>>>> 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 =3D 2. we hold on to issuing capture if more than 2 buffers are queued and it=20 continues only after fifo has min 1 slot empty