statistics Question

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Jay Gischer (gischer++at++puget.engr.sgi.com)
Thu, 2 Apr 1998 10:24:58 -0800 (PST)

Sam Chu writes:
> Dear Performers:
>
> In Perfly statistics I got: (two channels one pipe)
>
> 30/30 Hz
> ...
> MSecs: frame=50.6 app=3.7 cull=8.0 draw=6.7 isect=3.2
> Frames=60 Misses: total=0 app+cull=0 draw=0
>
> another channel
> MSecs: (almost the same as the above)
> Frames=61 Misses: total =61 app+cull=0 draw=0
>
> Question:
> 1. why app+cull+draw+isect much small than frame?
> 2. why 50.6(frame)*30Hz > 1000 MSecs(1 Sec)?
> 3. then what "frame:" means in "MSecs: frame=50.6"?
> 4. What Misses means? Does it mean how many frames Performer drop?
> 5. Why in one channel Misses=0 and another Misses=61?
>
> Thank for any reply in advanced.
>

The key realization here is that two channels are being drawn
sequentially on one pipe

I've taken the liberty of rephrasing the questions slightly for the
sake of clarity.

Q Why are the app+cull+draw+isect times much smaller than the frame
  time? What does "frame=50.6" mean anyway?

A. The app, cull, draw, isect times are measured times from beginning
  to end of phase for ONE channel. The Frame time is a cycle time,
  namely the time from the finish of one frame to the finish of
  the next frame of that ONE channel. So it includes the time to
  draw the other channel as well. In your case, app+cull+draw+isect
  add up to about 21.2, leaving 28.4 for the other frame and some
  possible overhead, which doesn't seem completely unreasonable.

Q.Why is 50.6 MSec * 30 Hz larger than 1000 MSec?

A. I'm not positive about this one, but I believe that "30Hz" is the
  target frame rate (which isn't being realized), rather.than the
  realized frame rate. Remember that gathering, and drawing stats actually
  takes a fair amount of time.

Q. What do "Misses" mean, and why does one channel have "Misses=0" and
   the other have "Misses=61".

A. A "Miss" is counted every time a channel does not finish drawing in
   time to make the target refresh cycle.
   Your app was missing its target frame rate (see previous question),
   But one of the channels was done in plenty of time to hit the frame
   rate, so it doesn't have any misses. The other one didn't finish
   in time, so it gets a "Miss" counted against it.

I hope that clarifies matters.

------------------------------------------------------------------------
Jay L Gischer + "I see great things in baseball. It's our game.
Advanced Graphics + It will repair our losses and be a blessing to
Software + us."
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                     + -Jackie Robinson

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