Re: [LKP] [lkp] [x86/hweight] 65ea11ec6a: will-it-scale.per_process_ops 9.3% improvement

[H. Peter Anvin]

On August 17, 2016 8:45:13 PM PDT, Borislav Petkov <bp@xxxxxxx> wrote:
>On Wed, Aug 17, 2016 at 03:29:04PM -0700, Huang, Ying wrote:
>> branch-miss-rate decreased from ~0.30% to ~0.043%.
>> 
>> So I guess there are some code alignment change, which caused
>decreased
>> branch miss rate.
>
>Hrrm, I still can't imagine how that would happen if the machine
>supports POPCNT and we never call the __sw_hweight* variants. Or does
>it?
>
>Can you paste /proc/cpuinfo from that Sandy Bridge-EP box?
>
>Thanks.

popcnt was introduced in Nehalem AFAIK, two generations before Sandy Bridge.
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