What is the memory bandwidth of modern CPU versus that of CUDA-enabled GPU?
As far as I figured it out, I thought GPU memory bandwidth was huge, but I thought that memory bandwidth of CPU L1-cache could be effectively better than actual CUDA architecture.
With all the horsepower delivered by CUDA GPU, up to 10X Gigaflops on GTX than current Core i7/Nehalem processors, we all need to be able to feed them with data and unload results as fast as possible in memory (global videocard memory or computer’s main memory).
I found an interesting article that benchmarked overclocked Core i7 cache and memory bandwidth, in triple-channel with fast DDR3: L1 cache peaks around 50GB/s reading or writing but could do both at once, peaking at 100GB/s, while main computer memory (triple-channel DDR3) was limited to 16 GB/s. That’s actually astonishing anyway, a 3 years old Athlon X2 3800+ (2×2Hz) L1-cache doesn’t deliver more than actual main memory of today!!!
To compare the L1 cache of a CPU (32KB), we should use CUDA Shared Memory (16KB/8 Scalar Processors), and it delivers around 50GB/s too, a value that is strangely similar.
To compare the main memory of the computer we have the Global Memory and it delivers between 100GB/s and 150GB/s, nearly 8X the computer’s main memory bandwidth, due to multiple 64-bits interface (8 instead 3) and higher clock values.
But when you test a shared memory access or a L1-cache access speed, you have to think there’s 4 core on a core i7, each one with it’s dedicated L1-cache, peaking at 200GB-400GB/s depending on the tasks.
On the other side, with 30 groups of 8 Scalar Processors, the Shared Memory of a CUDA GTX 285 may deliver 1500 GB/s, around 4X the aggregated L1-cache of an overclocked Core i7!
To resume, CUDA-enabled GPU offers up to 8X the speed of main memory and 4X the speed of L1-cache compared to a moderne CPU, and it shows!