Re: [patch, fortran] Enable FMA for AVX2 and AVX512F for matmul

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Mar 2, 2017 at 9:09 AM, Janne Blomqvist
<blomqvist.janne@gmail.com> wrote:
> On Thu, Mar 2, 2017 at 9:50 AM, Thomas Koenig <tkoenig@netcologne.de> wrote:
>> Am 02.03.2017 um 08:32 schrieb Janne Blomqvist:
>>>
>>> On Wed, Mar 1, 2017 at 11:00 PM, Thomas Koenig <tkoenig@netcologne.de>
>>> wrote:
>>>>
>>>> Hello world,
>>>>
>>>> the attached patch enables FMA for the AVX2 and AVX512F variants of
>>>> matmul.  This should bring a very nice speedup (although I have
>>>> been unable to run benchmarks due to lack of a suitable machine).
>>>
>>>
>>> In lieu of benchmarks, have you looked at the generated asm to verify
>>> that fma is actually used?
>>
>>
>> Yes, I did.
>>
>> Here's something from the new matmul_r8_avx2:
>>
>>     156c:       c4 62 e5 b8 fd          vfmadd231pd %ymm5,%ymm3,%ymm15
>>     1571:       c4 c1 79 10 04 06       vmovupd (%r14,%rax,1),%xmm0
>>     1577:       c4 62 dd b8 db          vfmadd231pd %ymm3,%ymm4,%ymm11
>>     157c:       c4 c3 7d 18 44 06 10    vinsertf128
>> $0x1,0x10(%r14,%rax,1),%ymm0,%ymm0
>>     1583:       01
>>     1584:       c4 62 ed b8 ed          vfmadd231pd %ymm5,%ymm2,%ymm13
>>     1589:       c4 e2 ed b8 fc          vfmadd231pd %ymm4,%ymm2,%ymm7
>>     158e:       c4 e2 fd a8 ad 30 ff    vfmadd213pd
>> -0x800d0(%rbp),%ymm0,%ymm5
>
> Great, looks good!
>
>> ... and here from matmul_r8_avx512f:
>>
>>     1da8:       c4 a1 7b 10 14 d6       vmovsd (%rsi,%r10,8),%xmm2
>>     1dae:       c4 c2 b1 b9 f0          vfmadd231sd %xmm8,%xmm9,%xmm6
>>     1db3:       62 62 ed 08 b9 e5       vfmadd231sd %xmm5,%xmm2,%xmm28
>>     1db9:       62 62 ed 08 b9 ec       vfmadd231sd %xmm4,%xmm2,%xmm29
>>     1dbf:       62 62 ed 08 b9 f3       vfmadd231sd %xmm3,%xmm2,%xmm30
>>     1dc5:       c4 e2 91 99 e8          vfmadd132sd %xmm0,%xmm13,%xmm5
>>     1dca:       c4 e2 99 99 e0          vfmadd132sd %xmm0,%xmm12,%xmm4
>>     1dcf:       c4 e2 a1 99 d8          vfmadd132sd %xmm0,%xmm11,%xmm3
>>     1dd4:       c4 c2 a9 99 d1          vfmadd132sd %xmm9,%xmm10,%xmm2
>>     1dd9:       c4 c2 89 99 c1          vfmadd132sd %xmm9,%xmm14,%xmm0
>>     1dde:       0f 8e d3 fe ff ff       jle    1cb7
>> <matmul_r8_avx512f+0x1cb7>
>
> Good, it's using fma, but why is this using xmm registers? That would
> mean it's operating only on 128 bit blocks at a time so no better than
> plain AVX. AFAIU avx512 should use zmm registers to operate on 512 bit
> chunks.
>
> I guess this is not due to your patch, but some other issue.

The question is, was it using %zmm before the patch?

>
> --
> Janne Blomqvist