Hi pekka >>are the c2p numbers from weston-presentation-shm demo? yes. I use this demo. My clock is CLOCK_MONOTONIC.
I check the drm kernel code, I find each vblank event send the last vblank's timestamp. system time sec msec [ 263.000526] vblank_event 262 983 [ 263.017236] vblank_event 263 0 [ 263.033864] vblank_event 263 17 [ 263.050533] vblank_event 263 33 [ 263.067215] vblank_event 263 50 I think that's should be the main reason cause the c2p time weird. I don't know why kernel return last frame's timestamp. I am still debuging it. Best Regards Nancy 2018-05-22 15:51 GMT+08:00 Pekka Paalanen <ppaala...@gmail.com>: > On Mon, 21 May 2018 23:06:12 +0800 > zou lan <nancy.lan....@gmail.com> wrote: > > > Hi pekka > > > > I debug the presentation time recently. I have checked each user call > > drmAtomicCommit get the corresponding pageflip event. > > But some presentation results (c2p) are a little weird. They are 1~5ms or > > -1 ~ -5 ms. some results are normal(8 ~ 20 ms). > > I used to explain the weird result is because pageflip return last > frame's > > timestamp, but I can't explain the normal results. > > > > I suspect whether the kernel and user have the same time start point. > It's > > just a guess, I have no evidence. > > > > Do you have some tips about the c2p results? Thank you. > > Hi Nancy, > > are the c2p numbers from weston-presentation-shm demo? > > The presentation-time extension has an event to tell the client which > clock domain is being used for the timestamps. This comes from DRM, > Weston attempts to enable CLOCK_MONOTONIC, but if your kernel is > ancient or otherwise weird, the default in DRM is CLOCK_REALTIME. > > Check your weston log for these lines: > presentation clock: CLOCK_MONOTONIC, id 1 > presentation clock resolution: 0.000000001 s > > If the resolution is much coarser than this, you have a kernel build > configuration issue. > > If all that checks out and you see the problem even with unmodified > weston, then I would suspect a driver bug, but it's hard to tell. > > You may want to grab a timeline recording and post that compressed. We > can then use wesgr to visualize it: > https://github.com/ppaalanen/wesgr > You can start and stop the recording by typing Mod+Shift+Space, 't'. It > writes a file to weston's current working directory and you see it > mentioned in the log as well. > > > The c2p times should really not vary much. On an intel GPU, with 60 Hz > display, the default mode of weston-presentation-shm gives me a steady > 23-24 ms c2p. This is the default repaint window setting. If I use the > low latency mode (-p), I get c2p 17-18 ms. (The intel driver can > actually send the pageflip event a little earlier than the timestamp it > carries, because it predicts the vblank when it's sure the presentation > will happen.) > > I also found a crash bug in Weston just now when playing with > weston-presentation-shm, probably related to a patch I recently landed. > > > Thanks, > pq >
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