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 11:58:52 -0700 |
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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.
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