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NN-512 is an open-source Go program that generates fully AVX-512 vectorized, human-readable, stand-alone C implementations of convolutional neural nets The gen

NN-512 is an open-source Go program that generates fully AVX-512 vectorized, human-readable, stand-alone C implementations of convolutional neural nets The generated C code is an example of AVX-512 programming using GCC's AVX-512 intrinsics. AVX-512 is exciting because its use of masking simplifies edge cases (partial loads, partial stores, etc.), there are 32 wide vector registers, and really excellent shuffle/permutation instructions (in particular, the two-input permute by var). Recent versions of GCC produce very good object code from C intrinsics The goal of NN-512 is efficient neural net inference on inexpensive, CPU-only cloud instances. For example, a Skylake-X cloud compute instance costs $10 per CPU-core per month at Vultr, and the NN-512 generated code does about 18 DenseNet121 inferences per CPU-core per second (in series, not batched) As AVX-512 becomes better supported by Intel and AMD chips, it becomes more attractive as an alternative to expensive GPU instances for workloads with small amounts of inference mixed with other computation

Rochus 6y ago
Great idea.
kevinventullo 6y ago
Out of curiosity, have you benchmarked this against some of the more standard NN libraries running on CPU?
- deleted 6y ago
  [deleted]
- 37ef_ced3 6y ago
  No, the convolution generators were written to saturate the hardware For example, under ideal conditions (no out-of-register memory access, no waiting on dependencies) you can sustain 27 single-precision FMADDs per CPU-core per cycle on a particular Skylake-X (i.e., approx 1.7 _mm512_fmadd_ps per cycle, each yielding 16 multiply-adds) As soon as you start accessing memory, that number drops to about 20 FMADDs. With direct convolution methods (1x1 and arbitrary), the best you can do is achieve that, and NN-512 comes close With the Fourier and Winograd convolutions, you start being limited by memory bandwidth, but the reduction in FMADDs that these methods provide means you end up ahead: your "effective" FMADD rate is much higher than what is possible through direct convolution. For example, NN-512 can exceed 48 effective FMADDs per cycle (on the 27 peak FMADD machine) with Winograd-Cook-Toom-Lavin, if the tensor is deep enough (enough channels) So, NN-512 succeeds in saturating the hardware. Essentially all the time is spent in the matrix multiplications, doing FMADDs, or being blocked bringing half-precision weights into register for Fourier or Winograd Until I generate a table of comparisons, you can use the previously stated number to do rough comparisons against the literature or other software packages: 18 DenseNet121 inferences per CPU-core per second on a cheap Skylake-X cloud instance
  - jklontz 6y ago
    > For example, NN-512 can exceed 48 effective FMADDs per cycle (on the 27 peak FMADD machine) with Winograd-Cook-Toom-Lavin, if the tensor is deep enough (enough channels) Roughly how many channels do you need for this approach to be worthwhile?
    - 37ef_ced3 6y ago
      Enough that the data panel of the input tensor fills the thread's share of the L2 cache, and the output tensor is of similar depth So it depends on the cache size, but you can think of it as being about 512 channels in, 512 channels out, something like that
colejohnson66 6y ago
Is there the option to use AVX2 (256-bit) instead of AVX-512 (which can cause thermal throttling on basically every chip[a])? Now, if Intel can get AVX-512 working well, that’s something else. Side question: do any Ryzen processors support AVX-512? AFAIK, they only support up to AVX2. [a]: IIRC, some tests show AVX2 code actually being faster than the equivalent AVX-512 code because AVX2 doesn’t cause the processor to throttle so hard
- aseipp 6y ago
  AVX2 also causes various degrees of thermal throttling depending on which chip you're using, such as Haswell. AVX-512 on Ice Lake (client) however is quite good and causes very little throttling versus its sustained speeds (e.g. my Ice Lake laptop @ 3.6GHz or whatever it is). Ultimately you have to do benchmarking yourself and if you care about inferences/sec you'll have to think about this stuff. That said, AVX2 support would also be cool simply because it's more readily available to use on more platforms, not just my laptop...
  - banachtarski 6y ago
    AVX-512 causes just as much if not more throttling in my experience? In what case are you finding that AVX-512 runs at lower voltages than AVX2?
- 37ef_ced3 6y ago
  No support for AVX2. AVX-512 is the first really nice (from the programmer's perspective) SIMD instruction set on x86-64 CPUs, and it's significantly different from what came before. AVX-512 is not just a wider version of AVX2 NN-512 explores the way Winograd and Fourier convolutions can be done when you have 32 512-bit vector registers. Four 8x8 Winograd tiles simultaneously, four 8x8 Fourier tiles interleaved to form a 16x16 tile for strided convolutions, and so on. These multi-tile operations don't work for AVX2, too few registers, each register too narrow GCC has only very recently come into a state where it properly supports AVX-512. For example, before GCC 9.1, GCC would split FNMADD into xor-negation followed by FMADD (doing an extra xor, using an extra register for the negation constant, instead of just using the FNMADD instruction). Eventually the hardware will mature, too
tintor 6y ago
Hi, how does it compare to https://github.com/pytorch/FBGEMM https://github.com/pytorch/FBGEMM?

Rochus 6y ago

Great idea.

kevinventullo 6y ago

Out of curiosity, have you benchmarked this against some of the more standard NN libraries running on CPU?

deleted 6y ago
[deleted]
37ef_ced3 6y ago
No, the convolution generators were written to saturate the hardware For example, under ideal conditions (no out-of-register memory access, no waiting on dependencies) you can sustain 27 single-precision FMADDs per CPU-core per cycle on a particular Skylake-X (i.e., approx 1.7 _mm512_fmadd_ps per cycle, each yielding 16 multiply-adds) As soon as you start accessing memory, that number drops to about 20 FMADDs. With direct convolution methods (1x1 and arbitrary), the best you can do is achieve that, and NN-512 comes close With the Fourier and Winograd convolutions, you start being limited by memory bandwidth, but the reduction in FMADDs that these methods provide means you end up ahead: your "effective" FMADD rate is much higher than what is possible through direct convolution. For example, NN-512 can exceed 48 effective FMADDs per cycle (on the 27 peak FMADD machine) with Winograd-Cook-Toom-Lavin, if the tensor is deep enough (enough channels) So, NN-512 succeeds in saturating the hardware. Essentially all the time is spent in the matrix multiplications, doing FMADDs, or being blocked bringing half-precision weights into register for Fourier or Winograd Until I generate a table of comparisons, you can use the previously stated number to do rough comparisons against the literature or other software packages: 18 DenseNet121 inferences per CPU-core per second on a cheap Skylake-X cloud instance
- jklontz 6y ago
  > For example, NN-512 can exceed 48 effective FMADDs per cycle (on the 27 peak FMADD machine) with Winograd-Cook-Toom-Lavin, if the tensor is deep enough (enough channels) Roughly how many channels do you need for this approach to be worthwhile?
  - 37ef_ced3 6y ago
    Enough that the data panel of the input tensor fills the thread's share of the L2 cache, and the output tensor is of similar depth So it depends on the cache size, but you can think of it as being about 512 channels in, 512 channels out, something like that

colejohnson66 6y ago

Is there the option to use AVX2 (256-bit) instead of AVX-512 (which can cause thermal throttling on basically every chip[a])? Now, if Intel can get AVX-512 working well, that’s something else. Side question: do any Ryzen processors support AVX-512? AFAIK, they only support up to AVX2. [a]: IIRC, some tests show AVX2 code actually being faster than the equivalent AVX-512 code because AVX2 doesn’t cause the processor to throttle so hard

aseipp 6y ago
AVX2 also causes various degrees of thermal throttling depending on which chip you're using, such as Haswell. AVX-512 on Ice Lake (client) however is quite good and causes very little throttling versus its sustained speeds (e.g. my Ice Lake laptop @ 3.6GHz or whatever it is). Ultimately you have to do benchmarking yourself and if you care about inferences/sec you'll have to think about this stuff. That said, AVX2 support would also be cool simply because it's more readily available to use on more platforms, not just my laptop...
- banachtarski 6y ago
  AVX-512 causes just as much if not more throttling in my experience? In what case are you finding that AVX-512 runs at lower voltages than AVX2?
37ef_ced3 6y ago
No support for AVX2. AVX-512 is the first really nice (from the programmer's perspective) SIMD instruction set on x86-64 CPUs, and it's significantly different from what came before. AVX-512 is not just a wider version of AVX2 NN-512 explores the way Winograd and Fourier convolutions can be done when you have 32 512-bit vector registers. Four 8x8 Winograd tiles simultaneously, four 8x8 Fourier tiles interleaved to form a 16x16 tile for strided convolutions, and so on. These multi-tile operations don't work for AVX2, too few registers, each register too narrow GCC has only very recently come into a state where it properly supports AVX-512. For example, before GCC 9.1, GCC would split FNMADD into xor-negation followed by FMADD (doing an extra xor, using an extra register for the negation constant, instead of just using the FNMADD instruction). Eventually the hardware will mature, too

tintor 6y ago

Hi, how does it compare to https://github.com/pytorch/FBGEMM https://github.com/pytorch/FBGEMM?