M1 GPU has higher FP32 than A-series GPUs

By: K.K (anon.delete@this.anon.com), December 9, 2020 4:56 am
Room: Moderated Discussions
Adrian (a.delete@this.acm.org) on December 9, 2020 2:16 am wrote:

> It does not matter how you name them, 2 FP16 ALUs that can be aggregated into 1 FP32
> ALU or 1 FP32 ALU that can be split into 2 FP16 ALUs are the same physical thing.

I understand what you are saying, but I think that it's neither of those things. My speculation is that the iPhones have FP16 ALUs that are capable of doing a FP32 operation at half the speed. So no ALU fusion, but ALU "reuse" (if it makes any sense). And that M1 upgrades the ALUs to full FP32 width, while retaining the ability to do a single FP16 operation (no ALU splitting taking place). Maybe M1 can't do FP16 at all use 32-bit precision internally all the way.

At any rate, you will find the benchmarks using interleaved FP32 and FP16 for an M1 and an A14 below. As far as I can tell from this, M1 does not have any ALUs capable of higher FP16 throughput — each combination runs with the same speed. I think this supports my theory of FP32 ALUs on M1, without any FP16 splitting. Note that this is different from the results I have reported earlier, but that was probably due a bug I have since fixed.

MacBook Pro (M1 with 8-core GPU)
--------------------------------
float1 + half1 2516.0
float1 + half2 2520.0
float1 + half3 2556.0
float1 + half4 2562.0
float2 + half1 2546.0
float2 + half2 2561.0
float2 + half3 2560.0
float2 + half4 2571.0
float3 + half1 2526.0
float3 + half2 2539.0
float3 + half3 2549.0
float3 + half4 2556.0
float4 + half1 2531.0
float4 + half2 2549.0
float4 + half3 2548.0
float4 + half4 2552.0


iPhone 12 (A14 with 4-core GPU)
--------------------------------
float1 + half1 1260.0
float1 + half2 1260.0
float1 + half3 1280.0
float1 + half4 1281.0
float2 + half1 967.0
float2 + half2 1280.0
float2 + half3 1277.0
float2 + half4 1287.0
float3 + half1 858.0
float3 + half2 1070.0
float3 + half3 1274.0
float3 + half4 1276.0
float4 + half1 807.0
float4 + half2 967.0
float4 + half3 1127.0
float4 + half4 1276.0


One curious thing is that interleaving FP32 and FP16 on the A14 performs better than expected. I would have thought that float+half should result in around 975 GFLOPS (average of
650 GFLOPS FP2 and 1300 GFLOPS for FP16), but we get almost full 1300 GFLOPS. I turned -ffast-math off, but maybe the compiler manages to sneak some sort of optimisation in there.

>
>
> Normally the FPU32 ALUs are considered the fundamental units in any GPU, because they can
> be used for any graphical application, why the FP16 ALUs are optionally used to enhance the
> performance of those particular applications where high visual fidelity does not matter,
> or there are other reasons that make errors less important, e.g. in ML applications.
>
> It is true that for applications specifically aimed only to the small smartphone screens,
> where the visual artefacts caused by errors are much less visible, it is much more common
> to take advantage of FP16, even when such a use would be unacceptable on a large display.
>
>
> This is not a good enough reason to consider FP16 as more important than FP32, especially
> in the case of the Apple GPUs, which are intended to be also used with larger displays.
>
>

< Previous Post in ThreadNext Post in Thread >
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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