Re: [PATCH v2 2/2] x86: Improve memmove-vec-unaligned-erms.S

Re: [PATCH v2 2/2] x86: Improve memmove-vec-unaligned-erms.S

[Sunil Pandey]

On Sun, May 23, 2021 at 8:40 PM H.J. Lu via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On Sun, May 23, 2021 at 8:15 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > This patch changes the condition for copy 4x VEC so that if length is
> > exactly equal to 4 * VEC_SIZE it will use the 4x VEC case instead of
> > 8x VEC case.
> >
> > Results For Skylake memcpy-avx2-erms
> > size, al1 , al2 , Cur T   , New T   , Win , New / Cur
> > 128 , 0   , 0   , 9.137   , 6.873   , New , 75.22
> > 128 , 7   , 0   , 12.933  , 7.732   , New , 59.79
> > 128 , 0   , 7   , 11.852  , 6.76    , New , 57.04
> > 128 , 7   , 7   , 12.587  , 6.808   , New , 54.09
> >
> > Results For Icelake memcpy-evex-erms
> > size, al1 , al2 , Cur T   , New T   , Win , New / Cur
> > 128 , 0   , 0   , 9.963   , 5.416   , New , 54.36
> > 128 , 7   , 0   , 16.467  , 8.061   , New , 48.95
> > 128 , 0   , 7   , 14.388  , 7.644   , New , 53.13
> > 128 , 7   , 7   , 14.546  , 7.642   , New , 52.54
> >
> > Results For Tigerlake memcpy-evex-erms
> > size, al1 , al2 , Cur T   , New T   , Win , New / Cur
> > 128 , 0   , 0   , 8.979   , 4.95    , New , 55.13
> > 128 , 7   , 0   , 14.245  , 7.122   , New , 50.0
> > 128 , 0   , 7   , 12.668  , 6.675   , New , 52.69
> > 128 , 7   , 7   , 13.042  , 6.802   , New , 52.15
> >
> > Results For Skylake memmove-avx2-erms
> > size, al1 , al2 , Cur T   , New T   , Win , New / Cur
> > 128 , 0   , 32  , 6.181   , 5.691   , New , 92.07
> > 128 , 32  , 0   , 6.165   , 5.752   , New , 93.3
> > 128 , 0   , 7   , 13.923  , 9.37    , New , 67.3
> > 128 , 7   , 0   , 12.049  , 10.182  , New , 84.5
> >
> > Results For Icelake memmove-evex-erms
> > size, al1 , al2 , Cur T   , New T   , Win , New / Cur
> > 128 , 0   , 32  , 5.479   , 4.889   , New , 89.23
> > 128 , 32  , 0   , 5.127   , 4.911   , New , 95.79
> > 128 , 0   , 7   , 18.885  , 13.547  , New , 71.73
> > 128 , 7   , 0   , 15.565  , 14.436  , New , 92.75
> >
> > Results For Tigerlake memmove-evex-erms
> > size, al1 , al2 , Cur T   , New T   , Win , New / Cur
> > 128 , 0   , 32  , 5.275   , 4.815   , New , 91.28
> > 128 , 32  , 0   , 5.376   , 4.565   , New , 84.91
> > 128 , 0   , 7   , 19.426  , 14.273  , New , 73.47
> > 128 , 7   , 0   , 15.924  , 14.951  , New , 93.89
> >
> > Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> > ---
> >  sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
> > index 5e4a071f16..a783da5de2 100644
> > --- a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
> > +++ b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
> > @@ -420,8 +420,8 @@ L(more_2x_vec):
> >         cmpq    $(VEC_SIZE * 8), %rdx
> >         ja      L(more_8x_vec)
> >         cmpq    $(VEC_SIZE * 4), %rdx
> > -       jb      L(last_4x_vec)
> > -       /* Copy from 4 * VEC to 8 * VEC, inclusively. */
> > +       jbe     L(last_4x_vec)
> > +       /* Copy from 4 * VEC + 1 to 8 * VEC, inclusively. */
> >         VMOVU   (%rsi), %VEC(0)
> >         VMOVU   VEC_SIZE(%rsi), %VEC(1)
> >         VMOVU   (VEC_SIZE * 2)(%rsi), %VEC(2)
> > @@ -440,7 +440,7 @@ L(more_2x_vec):
> >         VMOVU   %VEC(7), -(VEC_SIZE * 4)(%rdi,%rdx)
> >         VZEROUPPER_RETURN
> >  L(last_4x_vec):
> > -       /* Copy from 2 * VEC to 4 * VEC. */
> > +       /* Copy from 2 * VEC + 1 to 4 * VEC, inclusively. */
> >         VMOVU   (%rsi), %VEC(0)
> >         VMOVU   VEC_SIZE(%rsi), %VEC(1)
> >         VMOVU   -VEC_SIZE(%rsi,%rdx), %VEC(2)
> > --
> > 2.25.1
> >
>
> LGTM.
>
> Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
>
> Thanks.
>
> --
> H.J.

I would like to backport this patch to release branches.
Any comments or objections?

--Sunil