On Thu, Mar 2, 2017 at 9:09 AM, Janne Blomqvist <blomqvist.ja...@gmail.com> wrote: > On Thu, Mar 2, 2017 at 9:50 AM, Thomas Koenig <tkoe...@netcologne.de> wrote: >> Am 02.03.2017 um 08:32 schrieb Janne Blomqvist: >>> >>> On Wed, Mar 1, 2017 at 11:00 PM, Thomas Koenig <tkoe...@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