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zacwonder

AGP Performance

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My question maybe not directly connected with dx, but in some way it is How turning off AGP can affect rendering performance? I wrote dx9 app that performs tweening animation. Animated mesh has 12k verts and 24k faces. When I run the app on P4 1.4 GHz with 512MB RAM and Radeon9700Pro 128MB RAM (but with AGP turned off) in software vertex processing mode I get around 26 fps. The same mesh animated on P3 733MHz with 256MB RAM and Geforce2MX 32MB RAM card (with AGP on) in software proc. mode yields 40fps! Is it really the AGP that makes such a difference? If so, why? PS. In hardware vertex processing mode Radeon yields 143fps compared to 79fps of gf2mx. But how much faster Radeon would be with AGP on?

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Uh...Just you let you know, there''s no such thing as ''turning your AGP off'' because it''s the AGP bus that connects your video hardware to your computer. Perhaps you mean turning AGP Fast-Writes off? Or AGP 8x off? Can you clarify this?

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actually, what you are seeing is the crappyness of the original pentium 4 williamettes. the pentium 3 you have is actually a far better proccesor than that pentium 4(this is one reason the pentium 4 almost flopped when it first came out, as it was expensive, and was crap compared to an OLDER processor). not related to the topic: I would recommend you put that 9700 pro on the p3 or better yet plunk down some money for a newer cpu.

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Definietly I can''t turn off the agp;b
This thought stroke me few minutes after posting my message
I wrote this becaue that''s what my ati drivers tell me.
Could it be that turning off fast write is such a big difference?
It''s hard to believe that P4 1.4 GHz is slower than P3 733.

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12k vertices of say 64 bytes = 768kbytes =approx 1MB
that means (I know, it''s a shortcut) that FPS =approx agp bandwidth in MB per second. that can up to 1000 and certainly more than 100.
Are you sure there is no other bottleneck in you code? Are you using dynamic VBs, is your indexing cache friendly, are your vertices 32 or 64 bytes in size (apg friendly, incidently L1 friendly)
I guess you are more likely to be memory bandwidth bound than agp bound...
see how fast your ram is at random accesses. (write a small app where you create a 4MB array that you read and write randomly. If you are evil, perform unaligned cross 32 byte boundary operations, and cry as you realize how slow it is)

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quote:
It''s hard to believe that P4 1.4 GHz is slower than P3 733.


not at all, it''s the same reason a amd athlon @ 700 will beat your pentium 4, it does more work per clock cycle.

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