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 15:00:43 -0700 Message-ID: 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> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: Content-Language: en-US Sender: linux-clk-owner@vger.kernel.org To: Dmitry Osipenko , thierry.reding@gmail.com, jonathanh@nvidia.com, frankc@nvidia.com, hverkuil@xs4all.nl, sakari.ailus@iki.fi, helen.koike@collabora.com Cc: sboyd@kernel.org, linux-media@vger.kernel.org, devicetree@vger.kernel.org, linux-clk@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-tegra@vger.kernel.org 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=20 >>>>>>>> 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#L= 462=20 >>>>> >>>> process is put to sleep until the condition evaluates to true or=20 >>>> 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=20 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=20 the buffers. >> >> when every buffer is available as long as we are in streaming, we=20 >> should process it. >> >> So if wake up happens when list has buffer, it will be processed but=20 >> 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,=20 > we should process it. > > So capture thread processes as long as buffers are available from user=20 > space limiting 2 simultaneous trigger of captures and thread will be=20 > in sleep when capture buffers list is empty or no stop thread is=20 > signaled.