M1 GPU has higher FP32 than A-series GPUs

By: K.K (anon.delete@this.anon.com), December 9, 2020 6:01 am
Room: Moderated Discussions
Adrian (a.delete@this.acm.org) on December 9, 2020 4:28 am wrote:
> Regarding "So no ALU fusion, but ALU "reuse" (if it makes any sense)", in the case when you have 1:2 speed rate
> ratios, like for Apple A14, then it is certain that you have a FP32 ALU that is split into 2 FP16 ALUs.
>
> For the adder parts of the ALUs, using either the words "fusion" or "splitting" is irrelevant.
> You just have 32 1-bit adders and they are reconfigured between FP16 and FP32 just by
> changing the ways that the carries are propagated. The increased complexity of 1 FP32
> adder over 2 FP16 adders (e.g. due to carry lookahead) is negligible.
>
> However, 1 multiplier for FP32 has a larger size than 2 multipliers for FP16 (with more 1-bit adders, up to
> double, for 24-bit FP32 fractions vs. 11/12-bit FP16 fractions). So, when 2 FPU16 ALUs are fused, the smaller
> combined FP16 multipliers would have to be used twice, to generate partial products, so you would see a larger
> speed rate ratio, e.g. of 1:4, between FP32 and FP16, because you have only half as many FP32 ALUs after fusion
> and each ALU would need at least 2 cycles to generate the result for an FMA or FMUL operation.

Thanks, that is very interesting!

How were AMD and Nvidia doing it before they introduced dual-rate FP16 support? That is a fairly recent change if I am not mistaken, but those GPUs supported FP16 data since forever.

Is it possible that Apple supply went from fused FP16 (2xFP16 = 1xFP32) ALUs to just FP32 ALUs, and completely dropped FP16 support from the M1? That would mean that the calculation is always performed with 32-bit precision, but data gets converted as necessary when entering/leaving the ALU (i.e. a 16-bit operand is widened to 32-bit, operated upon with 32-bit precision and then rounded to 16-bit). Would there be a way to test this? My numerics is rather dusty, but I suppose that performing an operation with FP32 precision and then rounding it down to FP16 will result in the same accuracy as performing the operation with FP16 precision from the start...

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TopicPosted ByDate
M1 GPU microbenchmarks (peak FLOPS)K.K2020/12/05 03:31 AM
  M1 GPU microbenchmarks (peak FLOPS)K.K.2020/12/05 03:57 AM
  M1 GPU microbenchmarks (peak FLOPS)Adrian2020/12/05 04:00 AM
  M1 GPU microbenchmarks (peak FLOPS)Chester2020/12/05 10:39 AM
    M1 GPU microbenchmarks (peak FLOPS)K.K2020/12/06 03:46 AM
  M1 GPU microbenchmarks (peak FLOPS)Maynard Handley2020/12/05 12:12 PM
  M1 GPU has higher FP32 than A-series GPUsAndrei F2020/12/06 03:24 AM
    M1 GPU has higher FP32 than A-series GPUsK.K2020/12/06 03:49 AM
    M1 GPU has higher FP32 than A-series GPUsJeff S.2020/12/06 11:12 PM
      M1 GPU has higher FP32 than A-series GPUsK.K.2020/12/07 02:32 AM
        M1 GPU has higher FP32 than A-series GPUsJeff S.2020/12/07 10:29 PM
          M1 GPU has higher FP32 than A-series GPUsK.K.2020/12/09 01:35 AM
            M1 GPU has higher FP32 than A-series GPUsAdrian2020/12/09 02:36 AM
              M1 GPU has higher FP32 than A-series GPUsK.K.2020/12/09 02:59 AM
                M1 GPU has higher FP32 than A-series GPUsAdrian2020/12/09 03:16 AM
                  M1 GPU has higher FP32 than A-series GPUsK.K2020/12/09 04:56 AM
                    M1 GPU has higher FP32 than A-series GPUsAdrian2020/12/09 05:28 AM
                      M1 GPU has higher FP32 than A-series GPUsK.K2020/12/09 06:01 AM
                        M1 GPU has higher FP32 than A-series GPUsAdrian2020/12/09 06:37 AM
                          and beyond just the flops...anonymou52020/12/09 02:08 PM
                            and beyond just the flops...Doug S2020/12/09 03:06 PM
                              and beyond just the flops...Maynard Handley2020/12/09 04:05 PM
                                and beyond just the flops...Adrian2020/12/09 05:36 PM
                                and beyond just the flops...anonymou52020/12/09 08:28 PM
                                  and beyond just the flops...Maynard Handley2020/12/09 08:40 PM
                                    and beyond just the flops...anonymou52020/12/10 02:18 AM
                                      and beyond just the flops...anonymou52020/12/10 02:51 AM
                                      and beyond just the flops...Maynard Handley2020/12/10 09:53 AM
                                        and beyond just the flops...Megol2020/12/10 10:57 AM
                                          and beyond just the flops...Maynard Handley2020/12/10 12:16 PM
                                            and beyond just the flops...anonymou52020/12/10 04:12 PM
                                              and beyond just the flops...anonymou52020/12/10 04:24 PM
                                                and beyond just the flops...Maynard Handley2020/12/10 06:18 PM
                                                  and beyond just the flops...Maynard Handley2020/12/10 06:23 PM
                                                    and beyond just the flops...anonymou52020/12/10 09:59 PM
                                                    and beyond just the flops...Gabriele Svelto2020/12/11 01:57 AM
                                                      and beyond just the flops...Dummond D. Slow2020/12/11 09:52 AM
                                                        and beyond just the flops...Maynard Handley2020/12/11 09:57 AM
                                                          and beyond just the flops...Dummond D. Slow2020/12/11 10:00 AM
                                                            and beyond just the flops...Maynard Handley2020/12/11 11:22 AM
                                                              and beyond just the flops...Dummond D. Slow2020/12/12 09:13 AM
                                                                and beyond just the flops...Maynard Handley2020/12/12 01:41 PM
                                                                  and beyond just the flops...Dummond D. Slow2020/12/12 03:35 PM
                                                  and beyond just the flops...Dummond D. Slow2020/12/11 09:41 AM
                                                    and beyond just the flops...Maynard Handley2020/12/11 10:01 AM
                                                      and beyond just the flops...Dummond D. Slow2020/12/11 10:23 AM
                                                        and beyond just the flops...Dummond D. Slow2020/12/11 10:24 AM
                                              and beyond just the flops...Adrian2020/12/11 01:37 AM
                                                and beyond just the flops...Adrian2020/12/11 02:59 AM
                                                and beyond just the flops...Ungo2020/12/11 03:39 AM
                                                and beyond just the flops...Maynard Handley2020/12/11 10:07 AM
                                                  and beyond just the flops...Adrian2020/12/11 11:39 AM
                                                    and beyond just the flops...anonymou52020/12/11 03:01 PM
                                                    and beyond just the flops...David Hess2020/12/12 08:17 AM
                                                      and beyond just the flops...Jukka Larja2020/12/12 11:08 AM
                                                        and beyond just the flops...David Hess2020/12/12 11:36 AM
                                                          and beyond just the flops...Jukka Larja2020/12/12 09:45 PM
                                                            and beyond just the flops...David Hess2020/12/13 06:59 PM
                                                        and beyond just the flops...Adrian2020/12/12 03:11 PM
                                                          and beyond just the flops...Adrian2020/12/12 03:21 PM
                                                            and beyond just the flops...David Hess2020/12/13 07:02 PM
                              and beyond just the flops...useruser2020/12/09 09:38 PM
                                and beyond just the flops...anonymou52020/12/10 02:31 AM
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