memcpy performance regressions 2.19 -> 2.24(5)

[H.J. Lu]

On Mon, May 22, 2017 at 12:17 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Thu, May 18, 2017 at 1:59 PM, Erich Elsen <eriche@google.com> wrote:
>> Hi H.J.,
>>
>> I was on vacation, sorry for the slow reply.  The updated benchmark
>> still shows the same behavior, thanks.
>>
>> I'll try my hand at creating a patch that makes that variable
>> __x86_shared_non_temporal_threshold a tunable.  It will be necessary
>> to do internal experiments anyway.
>>
>
> __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?
>

Here is a patch to add support for
"glibc.x86_cache.non_temporal_threshold=number"
to GLIBC_TUNABLES.


-- 
H.J.
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