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long waiting time between cull and draw


 
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tomas259
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Joined: 03 Jul 2019
Posts: 2

PostPosted: Wed Jul 03, 2019 7:47 pm    Post subject:
long waiting time between cull and draw
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Hi,

We are experiencing that our application can get into a state where stuttering occurs (unable to sustain 60hz).

We observe a large period of waiting between the cull and the draw calls, which seems weird. See attached pic.

Sometimes one or more of the draw call are drawn further to the left ie. after 3ms. But there is always this big void where it looks like nothing is going on.

Anybody have a hint on how to debug this ?

...

Thank you!

Cheers,
Tomas
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tomas259
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Joined: 03 Jul 2019
Posts: 2

PostPosted: Tue Jul 23, 2019 1:17 pm    Post subject:
long waiting time between cull and draw
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Hi,

We are experiencing that our application can get into a state where stuttering occurs (unable to sustain 60hz).

We observe a large period of waiting between the cull and the draw calls, which seems weird. See attached pic.

Sometimes one or more of the draw call are drawn further to the left ie. after 3ms. But there is always this big void where it looks like nothing is going on.

Anybody have a hint on how to debug this ?

...

Thank you!

Cheers,
Tomas

------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=76364#76364




Attachments:
http://forum.openscenegraph.org//files/waiting_535.jpg




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robertosfield
OSG Project Lead


Joined: 18 Mar 2009
Posts: 12337

PostPosted: Tue Jul 23, 2019 4:28 pm    Post subject:
long waiting time between cull and draw
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Hi Tom,



From the on screen stats it looks like the GPU work is holding back the draw dispatch of the next frame, the last camera's draw GPU looking like the most obvious culprit.  It could be the FIFO is filling and then blocking, or it could be that there is sync in place that is holding back the next frame.


Given you are getting stuttering then my guess is that as things stand the GPU throughout is something to work on.  I don't know anything about your hardware, database and rendering requirements so I can't suggest any specific remedy.  Could you provide some more info.  For instance adding scene stats to the screenshot would help.



Robert.

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RichardHarrison
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Joined: 03 Jan 2019
Posts: 24
Location: France

PostPosted: Wed Jul 24, 2019 3:14 pm    Post subject:
long waiting time between cull and draw
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On 03/07/2019 21:47, Tomas Eilsoe wrote:
Quote:
We observe a large period of waiting between the cull and the draw calls, which seems weird. See attached pic.

I suspect that this is because of vsync; your frame rate is ~60hz which
is likely the monitor frequency.

With my system (AMD R9-290) I only get the orange "GPU" sections when
running with vsync; if I disable it (traits->vsync = false) then these
disappear and more than 60hz is possible so I generally lock to 60hz
application side by waiting the appropriate amount after rendering has
finished.

I generally run with vsync disabled because it seems there is something
about the AMD driver that causes a vsync wait between each camera; I
wrote some notes about this
http://chateau-logic.com/content/deferred-rendering-rembrandt-performance


Quote:
Anybody have a hint on how to debug this ?

Disable vsync and see what happens.




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