Re: [PATCH] x86: Update __x86_shared_non_temporal_threshold

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Thu, May 25, 2017 at 7:36 AM, H.J. Lu <hongjiu.lu@intel.com> wrote:
> __x86_shared_non_temporal_threshold was set to 6 times of per-core
> shared cache size, based on the large memcpy micro benchmark in glibc
> on a 8-core processor.  For a processor with more than 8 cores, the
> threshold is too low.  Set __x86_shared_non_temporal_threshold to the
> 3/4 of the total shared cache size so that it is unchanged on 8-core
> processors.  On processors with less than 8 cores, the threshold is
> lower.
>
> Any comments?

Any objections?

> H.J.
> ---
>         * sysdeps/x86/cacheinfo.c (__x86_shared_non_temporal_threshold):
>         Set to the 3/4 of the total shared cache size.
> ---
>  sysdeps/x86/cacheinfo.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/sysdeps/x86/cacheinfo.c b/sysdeps/x86/cacheinfo.c
> index 1ccbe41..3434d97 100644
> --- a/sysdeps/x86/cacheinfo.c
> +++ b/sysdeps/x86/cacheinfo.c
> @@ -766,6 +766,8 @@ intel_bug_no_cache_info:
>
>    /* The large memcpy micro benchmark in glibc shows that 6 times of
>       shared cache size is the approximate value above which non-temporal
> -     store becomes faster.  */
> -  __x86_shared_non_temporal_threshold = __x86_shared_cache_size * 6;
> +     store becomes faster on a 8-core processor.  This is the 3/4 of the
> +     total shared cache size.  */
> +  __x86_shared_non_temporal_threshold
> +    = __x86_shared_cache_size * threads * 3 / 4;
>  }
> --
> 2.9.4
>



-- 
H.J.