Re: performance on lock phase.

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Rob Jenkins (robj++at++sgi.com)
Fri, 05 Mar 1999 00:03:43 -0800

>I made a bench with perfly, on oNYX2 IR2 tripipe
>When I use free mode : the application runs at 30 Hz.
>When I use lock mode on 30 Hz: the application runs between 20/30Hz.
>(I lock the cull and draw process),

>How you can explain that?

This is an illustration from the PF course notes:

Video refresh 60Hz( 16.7 mS /frame )
Frame Rate 30Hz ( 33.3mS /frame )
Frame 1 overrruns

| ! | ! | ! | ! |
|-F0-|~>|-F1-------------|~~~~~>|-F2-|~>!-F3-----|~~~~~>! | FREE
| ! | ! | ! | ! |
|-F0-|~~~~~~~~~>|-F1-------------|~~~~~~~~~~~~~>|-F3-----|~~~~~>| LOCK
| ! | ! | ! | ! |

In FREE run, the draw can start as quickly as possible so no frame get
dropped ( in this case though frame rate will vary )

In LOCK F0 has to wait for a fixed frame boundary, then as F1 overruns
it hs to wait for another fixed frame boundary so gets even further
behind.

This isn't exactly what you are seeing but you get the idea, in your
test FREE run is managing to always get everything done in 33ms whereas
in LOCK the wait for a frame boundary is causing drops.

Cheers
Rob

-- 
________________________________________________________________
Rob Jenkins	Silicon Graphics 	mailto:robj++at++sgi.com

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