x86: Update __x86_shared_non_temporal_threshold
Commit Message
__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?
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(-)
Comments
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
>
On Tue, May 30, 2017 at 7:44 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> 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
>>
>
I will check it today.
@@ -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;
}