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: Wed, 8 Apr 2020 12:38:21 -0700 Message-ID: References: <1585963507-12610-1-git-send-email-skomatineni@nvidia.com> <760d071e-0cbc-b3eb-9231-fb9f9ecb44a6@nvidia.com> <9e317f65-8a02-3b15-cfec-8e0d8374130e@gmail.com> <97b35910-4c93-123a-43a0-eb14476ed0f3@nvidia.com> <84ad4e2d-6ac1-e1f4-1c55-5edaae850631@nvidia.com> <15a879b3-8fb9-6821-3cdc-104ba583ac12@gmail.com> <0c425505-347f-7418-af7e-d121fe0d06dc@nvidia.com> <1a31cd60-739f-0660-1c45-31487d2f2128@nvidia.com> <603084a5-249a-4fe2-3646-e9335ef9ab43@nvidia.com> <7895b9c6-f27d-8939-73d7-67d785e1a8b7@nvidia.com> <15d8b525-67b5-b437-f7fd-89f80cd0d9f6@nvidia.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-kernel-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 4/8/20 11:58 AM, Sowjanya Komatineni wrote: > > On 4/8/20 10:45 AM, Sowjanya Komatineni wrote: >> >> On 4/8/20 7:21 AM, Dmitry Osipenko wrote: >>> External email: Use caution opening links or attachments >>> >>> >>> 08.04.2020 03:00, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>> ... >>>>>>>> I suppose that taking a shot takes at least few milliseconds,=20 >>>>>>>> which >>>>>>>> should be unacceptable to waste. >>>>>>> As long as buffers are in queue we have to keep processing each >>>>>>> buffer and between buffers obviously we have to wait for previous >>>>>>> frames to finish and this why we have separate thread for frame >>>>>>> finish where we can have next buffer capture ready and issue while >>>>>>> previous frame memory write happens >>>>> Also we specified numbers buffers as 3 to vb2 queue. So this is rare >>>>> case but to prevent issuing more than 2 at a time as VI HW is only >>>>> double buffered and syncpt fifo max depth is 2 added this to be=20 >>>>> safer. >>>> To be more clear, when more buffers are enqueued from userspace always >>>> capture list will be full and thread will be busy in capture till=20 >>>> either >>>> error or stop stream request happens. >>>> >>> If kthreads take more than 1% of CPU time during capture (video) with >>> more than 2 buffers in queue, then it's not good and I think you should >>> do something about it. If kthreads stay at ~0%, then it should be okay >>> as-is. >> >> VI outstanding requests max can only be 2=C2=A0 as syncpt fifo depth is = 2=C2=A0=20 >> and waiting to issue next capture when already 2 captures are=20 >> inflight happens only during beginning of streaming where buffers=20 >> allocated go thru capture for first time after queuing. >> >> same buffers are returned to userspace after capture and same=20 >> allocated buffers will be queued back for subsequent captures. >> >> So this case of holding to issue single shot when already single shot=20 >> is issue for 2 frames simultaneous happens only during beginning of=20 >> start stream and also we set num_buffers to allocate for queue as 3=20 >> although 2 is good enough where we will not hit this case even during=20 >> streaming start with 2 buffers >> > As 2 buffers are good enough to be clear will update in v7 to use 2=20 > buffers so we don't need to check for more than 2 outstanding buffers. correction: With 3 buffers, as soon as buffer is available capture=20 starts. So right most times I see it waiting for few ms before 3rd=20 capture to get through. As only 2 frames single shot can be issued in sequence (inflight=20 requests), instead of waiting for 1 of the request to finish, we can use=20 2 buffers and avoid waiting as 2 buffers are good enough. Will change=20 this in v7.