Jay Gischer (gischer++at++puget.engr.sgi.com)
Mon, 6 Apr 1998 11:46:55 -0700 (PDT)
> I think the reason that app+cull+draw+isect(32.6) in much small than
> fram(96.3) is that the process in wait for the Transformation and Fill
> stage to finish. So May I say that app+cull+draw is just for the CPU stage?
>
The label "frame" appears to be causing a great deal of confusion
here. Recall the picture of Performer's pipe
APP | Frame 1 | Frame 2 | Frame 3 | Frame 4 | etc
CULL | | Frame 1 | Frame 2 | Frame 3 | etc
DRAW | | | Frame 1 | Frame 2 | etc
If 30.0 Hz is the target frame rate then the target from one pipe
stage boundary to the next is 33.3 ms.
However, the time reported with the label "frame" is a latency time,
and measures the time from when the frame starts the APP stage, to
when it completes the draw stage. Ignoring special cases, this time
is 3 times as long as the time for a single stage. Three time 33.3 is
100, so 96.3 is about right.
The app time of 0.4 means that the APP stage finished very quickly,
and then hung around for a long time waiting for the next pfSynch(),
so it could start the CULL stage. Likewise for the cull time.
For each of the stages, Performer measures the time from the beginning
of that stage for the frame to when it completes its work, not to the
synch boundary, since that wouldn't be a very interesting number
Here's the picture again with annotations for what time each of
the stats measures.
APP | Frame 1 | Frame 2 | Frame 3 | Frame 4 | etc
app |<----->A1
CULL | | Frame 1 | Frame 2 | Frame 3 | etc
cull |<------>C1
DRAW | | | Frame 1 | Frame 2 | etc
draw |<---->D1
frame |<-------------------------->D1
A1 = APP stage completes on frame 1
C1 = APP stage completes on frame 1
D1 = Draw stage completes on frame 1
But this begs the question, why, if my draw time is 31.3, and my
latency is 96.3, am I not getting a frame rate of 30hz?
As it turns out, in perfly there are two contributions to the DRAW
stage which are not measured by the perfly stats, pre-draw and
post-draw.
In perfly, the GUI is drawn in the pre-draw phase, and statistics are
drawn in the post-draw phase. Together, they could easily take up
enough time (about 2 msecs) to push your application over the 33.3 ms
mark. The printed displays do not measure these times, but you can
glean this information from the graphical display by noticing that the
line representing the DRAW stage of a frame doesn't start quite at the
boundary (because of the pre-draw time before it), and is extended by
a dotted line after it (representing post-draw time).
The draw time *does* include transformation and fill.
Okay, so if that explains why we are running at 15hz instead of 30,
then why isn't the latency equal to about 66.6+66.6+31.3 = 164.5?
This is because you are running in LOCK mode. In LOCK mode, the
picture I gave above gets more complicated (assuming you are missing
the target rate in the draw stage):
APP | F1 | F2 | F3 | F4 | F5 | F6 | F7 | F8 | etc
app |<-->A1
CULL | | F1 | F2 | F3 | F4 | F5 | F6 | F7 | F8 | etc
cull |<-->C1
DRAW | | | F1 | F1 | F3 | F3 | F5 | F5 | F7 | F7 | etc
draw |<------->D1
frame |<------------------->D1
In LOCK mode the APP and CULL stages start each frame at the target
frame rate, and the DRAW stage merely ignores frames that it wasn't
ready to draw at the proper time, hence, in your case, it displays
only every other frame. But the latency from beginning of pipe to end
is smaller, on the order of 33.3+33.3+31.2 = 97.8 which is very close
to the reported latency of 96.3.
> If the above is true, how can I measure the time spent in the
> Transformation stage and Fill stage?
>
So, to summarize, the missing time (about 2ms) is due probably to GUI
and the stats display rendering. It is not due to fill time, which is
measured and included in the "draw" time.
------------------------------------------------------------------------
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."
Silicon Graphics + -Walt Whitman
(415) 390-4277 +
gischer++at++sgi.com + "A life has no meaning except in the impact it
+ has on other lives"
+ -Jackie Robinson
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