Re: [PATCH] x86: Update __x86_shared_non_temporal_threshold

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

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.

-- 
H.J.