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Journeyman III

Theoretical peak FLOPS

I have question regarding the theoretical peak FLOPS of my graphics card.

I have a Radeon HD 7970 GHz Edition which has a peak of 4096 GFLOPS.

Now I would wanted to calculate this number.

When I just multiply the core clock (1000 MHz) with the number of cores (2048) I get 2048 GFLOPS.

What am I missing to get the 4096 FLOPS? Does a MAD operation count as two operations?

Then again according to the AMD Accelerated Parallel Processing OpenCL Programming Guide it can execute 4 MAD, ADD or MUL operations per cycle (Page 5-23)?

Which would mean the number of FLOPS would be even higher.

Can someone explain how to calculate the theoretical peak FLOPS?

Many thanks!


2 Replies

yes MAD is counted as two operations. one cycle is executed in four clock as it executes 64 wide wavefront in four clocks.

Adept II

Part of the ever-existing confusion is that the terminology is dependent on context. When talking about the Southern Islands / GCNs, the 7970 has 32 Compute Units (CUs), each CU has 4 SIMDs, and each SIMD having 16 Processing Elements (ALUs).  So simple.. with a FMA counting as 2 ops/cycle, that gives you 4096 flops. But some of the documentation in the Southern Islands docs (like the table on 5-23) is more structured as if it was still talking about the Evergreen and Northern Islands chips where the Compute Unit is described as 16 Stream Processors (SP) and the SP does 4 ops per cycle.