Processor Cache Question

[Smalerbi]

Hello all,

I have a question about processor cache. I'm having a new system built and could someone please explain how important processor cache size is when it comes to Vray and Max? I'm noticing that cache size can play a large part on how much the xenon processor will end up costing. For example, 8 core processors will vary in price depending on how much Cache is in the chip. I'm not sure where the tipping is at.

Thanks

Scott.

[savage309]

Processors are fast. Main (ram) memory is super slow. The cache is your fast memory - the memory you need most usually is there. If you have a lot of it, the CPU will wait less for RAM memory access and work more (if I remember correctly, it is usually 1-10ns for cache read (depending on what cache you are reading) vs 100 for RAM read). Because of that, it is happens a lot for a developer to optimize not algorithm or calculations, but memory access.

So it is important, not only for vray but generally for all applications. The cache is small and expensive, but usually it is worth it.

After all the best way to tell, is if somebody can test it for you. Often what is on paper is not exactly what happens.

[Smalerbi]

Processors are fast. Main (ram) memory is super slow. The cache is your fast memory - the memory you need most usually is there. If you have a lot of it, the CPU will wait less for RAM memory access and work more (if I remember correctly, it is usually 1-10ns for cache read (depending on what cache you are reading) vs 100 for RAM read). Because of that, it is happens a lot for a developer to optimize not algorithm or calculations, but memory access.

So it is important, not only for vray but generally for all applications. The cache is small and expensive, but usually it is worth it.

After all the best way to tell, is if somebody can test it for you. Often what is on paper is not exactly what happens.

Thank you.........very useful information.

[MoonDoggie]

Main (ram) memory is super slow.

This is relative. If you're talking about on die RAM like L2 cache, then yes, it's slower. But in regards to relative speeds, RAM is incredibly fast...Compared to something like HD accesses, etc. Good luck even saturating the bandwidth for your RAM.

[vlado]

If you're talking about on die RAM like L2 cache, then yes, it's slower. But in regards to relative speeds, RAM is incredibly fast...Compared to something like HD accesses, etc. Good luck even saturating the bandwidth for your RAM.

I can assure you that there's plenty of places in the V-Ray code where the CPU is sitting idle waiting for data to arrive from the main RAM

Best regards,
Vlado

[MoonDoggie]

Noted. I was just thinking of HD bottlenecks and pointing out how huge that bottleneck is compared to RAM. You know best as always .