A Gamecube question

[Wildstyle]

Hay guys I was just wondering how much of the texture cache the GC uses in a real time game senario I have heard that it only uses a little bit of it during a frame or something like that and maybe you guys could give me some figures if possable.

 

[Teasy]

Where did you hear that? I don't see any reason for it to be true. The 1mb cache wouldn't be there if it could be used as a 1mb cache.

 

[Steve Dave Part Deux]

AFAIK management of the texture cache is transparent to the programmer.

 

[Wildstyle]

I never said the texture cache couldn't be used all I heard is that the GC doesn't use all of it during a scene and it may only use a lot or a little of it and I was just wondering how much would be a little and how much would be alot.

 

[Teasy]

But surely "I have heard that it only uses a little bit of it during a frame" means it can't use any more then a little bit. Unless you mean it only uses a little bit in current games or a specific game?

 

[Wildstyle]

I am kind of confused on your last post there Teasy maby you can enlightin me. As far as I know the GC doesn't use all of it's TC in any game?. But like how much would it use on a normal scene is basically what I am asking maybe you could give me a percentage or something.

 

[PC-Engine]

Are you talking about it's virtual texturing capabilities?

 

[Wildstyle]

Yeah I guess what's virtual texturing I wouldn't know I am kind of new to this big technical stuff.

 

[Crazyace]

The gamecube will use all of it's texture cache in a game - that's why it's a cache. ( It's a bit like saying that Photoshop doesn't use all of the L2 cache on a pentium )
All textures are stored in memory, and when the drawing engine requests a texture a small block is pulled from mainmem into the cache where the individual texels can be read at fullspeed. If the same texels are used again they are already in cache so don't hit main memory. ( Exactly the same technique is used on the Xbox although the details aren't disclosed )

 

[Wildstyle]

Hmm I still don't get how it would uses all of its cache when the main memory only has 1.3gbs of textures to pass to the cache. Unless the GC uses the same set of textures like 8 times per scene/frame is that how it works?

 

[V3]

Hmm I still don't get how it would uses all of its cache when the main memory only has 1.3gbs of textures to pass to the cache. Unless the GC uses the same set of textures like 8 times per scene/frame is that how it works?

Well, if you have broad bandwidth, than you can get away with small cache. If you have narrow bandwidth you want as much cache as you can get.

 

[clem64]

Where are you getting that 1.3 from? Main mem bandwidth minus bandwidth used by the CPU?

Well first of all it's not always 1.3. The CPU will probably never use 100% of the bandwidth it has access to. So whatever is not used can be used for textures. And second, this doesn't really affect how much of the texture cache on the GPU is used. The 1MB cache has around 10 GB/sec. of bandwidth for the GPU to work with. That is more then enough to work with anything in the cache.

The only scenario that I can think of where the cache wouldn't be used entirely would be if the scene being rendered would use less then 1MB of textures. In that case main RAM wouldn't be used at all for textures and the rest of the cache either. Very unlikely though given the GC's texturing capabilities. No developer in their right mind would use less then a MB worth of textures.

 

[Jabjabs]

The badwidth is probably more like 1.5GB per second as the CPU doesn't need to use 100% of it's FSB all the the time.