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 12:38:21 -0700 |
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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.
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