Messages in this thread | | | Subject | Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver | From | Sowjanya Komatineni <> | Date | Wed, 8 Apr 2020 20:38:43 -0700 |
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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 пишет: >>>> ... >>>>>>>>> I suppose that taking a shot takes at least few milliseconds, >>>>>>>>> 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 >>>>>> 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 >>>>> 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 as syncpt fifo depth is >>> 2 and waiting to issue next capture when already 2 captures are >>> inflight happens only during beginning of streaming where buffers >>> allocated go thru capture for first time after queuing. >>> >>> same buffers are returned to userspace after capture and same >>> allocated buffers will be queued back for subsequent captures. >>> >>> So this case of holding to issue single shot when already single >>> shot is issue for 2 frames simultaneous happens only during >>> beginning of start stream and also we set num_buffers to allocate >>> for queue as 3 although 2 is good enough where we will not hit this >>> case even during streaming start with 2 buffers >>> >> As 2 buffers are good enough to be clear will update in v7 to use 2 >> 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 > starts. So right most times I see it waiting for few ms before 3rd > capture to get through. > > As only 2 frames single shot can be issued in sequence (inflight > requests), instead of waiting for 1 of the request to finish, we can > use 2 buffers and avoid waiting as 2 buffers are good enough. Will > change this in v7. > > > Tested with 3 buffers and by checking outstanding buffers in process by VI hw and holding to start capture till one outstanding buffer in 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%
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