# Calculating Peak FMA throughput on CPUs

By: anonymous2 (anonymous2.delete@this.example.com), December 3, 2018 8:10 am
There has been a lot of interesting discussion on AVX2/AVX-512 of late but I'm still unclear how to calculate the peak theoretical FMA (DP) throughput for a given CPU.

For an AVX-512 FMA that's 8 DP (64-bit) FMA's per cycle (I'm talking FMAs, not doing the "count FMA as two FLOPS" thing), so 8*2 = 16 per cycle.

Taking a specific example:

It looks like the fastest cores are Intel Xeon W/HEDT with two AVX-512 units.

https://en.wikichip.org/wiki/intel/xeon_gold/6154

It looks like if all cores are doing AVX512 they will clock to 2.7GHz, so we have:

(8*2) * 18 * 2.7 GFLOP = 777.6 GFLOPs

Does that sound right?

AVX2 operations are only half as wide and still only two per cycle (I'm assuming this, I would like confirmation), but would run the core at a 3.3GHz giving

(4*2) * 18 * 3.3 GFLOP = 475.2 GFLOPS

What about for a Core i7-8700K? Wikichip doesn't list the AVX2 frequencies so I will assume it's the base frequency not less, having AVX2 only:

(4*2) * 6 * 3.7 GFLOP = 177.6 GLOPS

Do those numbers look plausible? Do I have a multiplier wrong somewhere?

Thanks!
TopicPosted ByDate
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