The AMD Vega GPU Architecture Tech Report

Page 2 : High-Bandwidth Cache, HBM2 Memory, Cache Controller, Why Is It Called A Cache?

High-Bandwidth Cache

AMD Vega will use HBM2 memory, as well as a new High-Bandwidth Cache Controller (HBCC). Together, they are known as the High Bandwidth Cache.

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AMD showcased the performance of the High-Bandwidth Cache using a real-time render of Joe Macri’s living room on Radeon ProRender with 700+ GB of data. Although no frame rate was visible, the real-time render appeared to be very smooth.

 

The HBM2 Memory

HBM2 offers twice the transfer rate per pin (up to 2 GT/s), over its the first-generation HBM memory. This allows it to achieve up to 256 GB/s memory bandwidth per package.

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In both HBM and HBM2, up to 8 memory dies can be stacked in a package. But moving to HBM2 allows for twice the memory density – up to 8 GB per package is now possible.

 

The High-Bandwidth Cache Controller

The second component of the High Bandwidth Cache is the new High-Bandwidth Cache Controller (HBCC). It creates a homogenous memory system for the AMD Vega GPU, with up to 512 TB of addressable memory.

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It also allows for the adaptive, fine-grained movement of data between the AMD Vega GPU and the system memory, the NVRAM and the network storage (as part of Infinity Fabric).

 

Why Is It Called A Cache?

AMD calls the combination of the HBM2 memory and the High-Bandwidth Cache Controller the “High-Bandwidth Cache“. Techies may wonder why AMD chose to call it “cache”, instead of “memory”. After all, HBM2 memory is a type of fast graphics memory.

The answer lies in the AMD Vega’s heterogenous memory system. All memory in the system, whether it’s the HBM2 memory or shared memory from the computer’s SDRAM, is seen as a contiguous memory space. A big block of memory, irrespective of how fast they are.

That may be great for memory addressing, but may cause frequently-used data to be placed in slower memory. To avoid such an occurrence, the High-Bandwidth Cache Controller uses the HBM2 memory like a fast cache. This allows it to keep the most frequently-used data in the fastest memory available – the HBM2 memory.

Hence, the HBM2 memory functions like a cache in AMD Vega, and that is why AMD called the combination the High-Bandwidth Cache.

Next Page > The New AMD Vega Geometry Pipeline, Compute Unit & Pixel Engine

 

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