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FPS slowdown

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Hi everyone! i have a scene with 2 polygons... YES 2!... each polygon has a lightmap and a texturemap. But i am getting severe fps shortage when i get near the polygons?? Any idea why? its only since i added the multitexturing code that its done it. Paul

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With servere FPS shortage you mean, what? From 85 to 10 FPS ?
And what gfx-card has the shortage occured with? Because the older cards has of cause a problem with running multitexturing, but newer cars, like Geforce or Radeon, shouldn''t have...So if you are sitting with an old card, like an onboard Voodoo or whatever, then it''s quite realistic that the FPS drops a lot.

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Measuring fps on a gpu card with only 2 polygons isnt very usefull. And remember to measure milliseconds between frames instead of FPS since a slowdown from 4000fps to 2000fps is MUCH less than a slowdown from 20fps to 10fps

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my card is a geforce3ti200, the fps drop is 60.0 to about 15-20.
Im not testing fillrate of the card, i have just implemented lightmapping, and i am testing it on two polygons.

I just noticed a huge drop in fps when i get close to the polys. It does seem like a fill-rate thing, but its two textures, two polys and a geForce3! it shouldn''t drop fps at all, let alone 40...

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almost similar problem for me.
the fps is always high except that when i go near ms3d model loaded.fps drops very low right then.
would be happy if anyone can tell how to keep the fps high.

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As others said - it primarily sounds like a fillrate problem.

Also, I noticed the fps numbers you mentioned: "the fps drop is 60.0 to about 15-20" Do you have vsync on? Values 60,20,15 make me think it might be on by accident and I was just asking to eliminate this possibility.

On the other side, 2 polies is indeed a very poor test. If you have the time to go thru a pdf, search on nvidia''s developer site for one named BatchBatchBatch. It will explain why a two poly test gives horrible results. You are spending a disproportionate time in just submitting the two polies - meaning your app could easily be cpu-bound as well by this "simple" test. For example, they tested various cards (GF2 MX and up) and found that under 130 tris/batch you are (and I quote):
- completely,
- utterly,
- totally,
- 100%

- CPU limited!

CPU is busy doing nothing, but submitting batches!


Another article, one that touches on the GF3 family, is GDC2002_PipePerformance.pdf at nvidia''s site. Check out other articles as well.

I came across a similar issue recently with my own code - except I was trying to obtain maximum fillrate at lower resolutions. After reading the BatchBatchBatch article I started to see how my test scene was inadequate (although it had 38K polies). Another way to look at it - I was misinterpreting the results of my own test.

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Guest Anonymous Poster
Its definately not a "disproportionate time in just Submitting the two polies " - it TWO POLYGONS!! There is no overhead! That nVidia document is about batch sizes and CPU overhead. It doesn''t apply here...

Anyway, the problem was a driver problem.....
cheers for the replys
Muncher

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Of course those articles don''t explain the low fps. I did err in saying that your 2 poly test could be cpu-bound - I meant to imply that submitting only a few polys (per batch) is a bad test for comparing fps to poly counts. I was really commenting on what you said: "scene with 2 polygons... YES 2!..."

A single batch of 2 polys or 2000 - it had no bearing on your problem. A 2 poly test simply means the amount of geometry can''t be causing the problem - nothing unusual in that respect. The batch article explains why "I get only X fps yet I have only N tris" has much less bearing on the number of tris than it did with older cards. Your first post sounded just like that and I thought you might find the article handy in the future. ie: Don''t expect any decent fps performance if in a real scene you also submit lots of low poly batches. Sorry if I wasn''t more clear on that part of my post.

Anyways - glad to hear you solved it.

Just out of curiosity what are your fps now?

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