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 20:38:43 -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-tegra-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 4/8/20 12:38 PM, Sowjanya Komatineni wrote: > > 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=20 >>>>> 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=20 >>>> 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= =20 >>> 2=C2=A0 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=20 >>> shot is issue for 2 frames simultaneous happens only during=20 >>> beginning of start stream and also we set num_buffers to allocate=20 >>> for queue as 3 although 2 is good enough where we will not hit this=20 >>> case even during 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=20 > use 2 buffers and avoid waiting as 2 buffers are good enough. Will=20 > change this in v7. > > > Tested with 3 buffers and by checking outstanding buffers in process by=20 VI hw and holding to start capture till one outstanding buffer in=20 process by HW. Also tested with 2 buffers without checking for outstanding buffers. In both cases, I see same %CPU for the kthreads and is < 1%