答复: [RFC PATCH 3/3] x86: Enable non-temporal memset for Hygon processors

[Feifei Wang]

> -----邮件原件-----
> 发件人: H.J. Lu <hjl.tools@gmail.com>
> 发送时间: 2024年8月12日 21:12
> 收件人: Feifei Wang <wangfeifei@hygon.cn>
> 抄送: libc-alpha@sourceware.org; carlos@redhat.com; fw@deneb.enyo.de;
> goldstein.w.n@gmail.com; Jing Li <lijing@hygon.cn>
> 主题: Re: [RFC PATCH 3/3] x86: Enable non-temporal memset for Hygon
> processors
> 
> On Sun, Aug 11, 2024 at 11:49 PM Feifei Wang <wangfeifei@hygon.cn> wrote:
> >
> > This patch is based on the following new flag patch:
> > https://patchwork.sourceware.org/project/glibc/patch/20240811055619.28
> > 63839-1-goldstein.w.n@gmail.com/
> 
> Please wait until the above patch has been reviewed and committed.
> 
That's fine.
> > After the new cpu-flag 'Prefer_Non_Temporal' is added in glibc, this
> > patch can be enabled to access the non-temporal memset implementation
> > for hygon processors.
> >
> > Test Results:
> > thread: 1
> > memset store value: 0
> >
> > hygon1 arch
> > x86_memset_non_temporal_threshold = 8MB
> > size                          new performance / old performance
> > 128 byte(2x -4x vec case)     1
> > 256 byte(4x - 8x vec case)    1
> > 512 byte( > 8x loop case)     1
> > 1MB                           0.994
> > 4MB                           0.996
> > 8MB                           0.670
> > 16MB                          0.343
> > 32MB                          0.355
> >
> > hygon2 arch
> > x86_memset_non_temporal_threshold = 8MB
> > size                          new performance / old performance
> > 128 byte(2x -4x vec case)     1
> > 256 byte(4x - 8x vec case)    0.653
> > 512 byte( > 8x loop case)     0.713
> > 1MB                           1
> > 4MB                           0.887
> > 8MB                           1.312
> > 16MB                          0.822
> > 32MB                          0.830
> >
> > hygon3 arch
> > x86_memset_non_temporal_threshold = 8MB
> > size                          new performance / old performance
> > 128 byte(2x -4x vec case)     1
> > 256 byte(4x - 8x vec case)    1
> > 512 byte( > 8x loop case)     1
> > 1MB                           1
> > 4MB                           0.990
> > 8MB                           0.737
> > 16MB                          0.390
> > 32MB                          0.401
> >
> > For hygon arch with this patch, no performance degradation on '2x - 8x branch
> case'
> > when extra branch jump added. And with this patch, non-temporal stores
> > can improve performance by 20% - 65%.
> >
> > Signed-off-by: Feifei Wang <wangfeifei@hygon.cn>
> > Reviewed-by: Jing Li <lijing@hygon.cn>
> > ---
> >  sysdeps/x86/cpu-features.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
> > index 034dc28f64..cae26babc7 100644
> > --- a/sysdeps/x86/cpu-features.c
> > +++ b/sysdeps/x86/cpu-features.c
> > @@ -1098,6 +1098,12 @@
> https://www.intel.com/content/www/us/en/support/articles/000059422/proce
> ssors.ht
> >        get_extended_indices (cpu_features);
> >
> >        update_active (cpu_features);
> > +
> > +      /* Use Prefer_Non_Temporal flag to access the non-temporal
> > +        memset implementation due to ERMS is disable in Hygon
> > +        processors.  */
> > +      cpu_features->preferred[index_arch_Prefer_Non_Temporal]
> > +      |= (bit_arch_Prefer_Non_Temporal);
> >      }
> >    else
> >      {
> > --
> > 2.43.0
> >
> 
> 
> --
> H.J.