Table 2. Speedup attained by the tested GPUs for three-dimensional (3D) FFT computations at different cube sizes.

		CPU
		K620		GTX 1080		Titan X		K20m		K80
Cube size	Time per 3D FFT (ms)	Speedup	Speedup per $1000	Speedup	Speedup per $1000	Speedup	Speedup per 1000$	Speedup	Speedup per $1000	Speedup	Speedup per $1000
32	5.8	35×	176	45×	64	49×	27	38×	17	100×	23
64	6.2	16×	78	45×	65	50×	28	39×	18	102×	23
128	68.3	14×	71	131×	188	179×	100	78×	36	198×	43
256	566.0	13×	67	178×	254	261×	145	100×	45	236×	54
512	6719.8	—	—	137×	296	202×	112	73×	33	178×	40