Recently I did some tests about GDDR5 memory bandwidth.
In a few words:
It launches numberOfCUes*4 waveFronts. Each WF is reading 1024 bytes from a random aligned location in a large buffer.
The whole kernel reads 100GB total. The ideal bandwidth is 1.850GHz*256bit/8*4=236.8GBps
I'm varying the buffer size from 1KB to 4GB and got the following results:
You can easily spot to 2 cache levels on it. But I've found a third something above 1GB.
Anyone has an explanation what is that?
I have 8GB and I only tested this up until 4GB, but it seems like if I use the whole memory, the bandwidth will settle at 1/3 of the nominal bandwidth.
This behavior with PC memory would be unacceptable for sure. But what's the case with graphics memory?
Thank You for the answers!