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<760d071e-0cbc-b3eb-9231-fb9f9ecb44a6@nvidia.com> <9e317f65-8a02-3b15-cfec-8e0d8374130e@gmail.com> From: Sowjanya Komatineni Message-ID: <97b35910-4c93-123a-43a0-eb14476ed0f3@nvidia.com> Date: Mon, 6 Apr 2020 16:48:41 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <9e317f65-8a02-3b15-cfec-8e0d8374130e@gmail.com> X-Originating-IP: [172.20.13.39] X-ClientProxiedBy: HQMAIL107.nvidia.com (172.20.187.13) To DRHQMAIL107.nvidia.com (10.27.9.16) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Content-Language: en-US DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1586216911; bh=HLb6nrvQHJ/9ja5w0a+AOxh5Qft5XGAcZe0yo4nGdxo=; h=X-PGP-Universal:Subject:To:CC:References:From:Message-ID:Date: User-Agent:MIME-Version:In-Reply-To:X-Originating-IP: X-ClientProxiedBy:Content-Type:Content-Transfer-Encoding: Content-Language; b=JC33UhAvmPHRLVyhkXd76e3gzOBCpwUW7OBLZ/5PlqX/t8BRQupAsntTMoGqSdleW azJuY4ZlmR8krQ9Mtyhf8+CyCfdb4EaUk3XF4bd5ihRcXyyoWUEUUY0KzPdpIkW47S 2929qI6ehhGrdf6Xp1cze5dEmgaZSMqeAewbRPM1Yh/pFjZ4Z3UaenBT8PwwVe5t+i IgcIzLHC705dgqVbZTUVhIOCPagUBUeLnMCbe+bGlxSS4aL2Vq1e3BGYcDqp6Iue0N I6D6hBXHMwTRarG0DPmfAtTzqQCCwrv/iDFDfBsI8Fy9AzC/7w8UttPOGQSIcq7gIm eL43wkJdo3HHA== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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