Borislav Petkov <[email protected]> writes:
> On Tue, Aug 16, 2016 at 04:09:19PM -0700, H. Peter Anvin wrote:
>> On August 16, 2016 10:16:35 AM PDT, Borislav Petkov <[email protected]> wrote:
>> >On Tue, Aug 16, 2016 at 09:59:00AM -0700, H. Peter Anvin wrote:
>> >> Dang...
>> >
>> >Isn't 9.3% improvement a good thing(tm) ?
>>
>> Yes, it's huge. The only explanation I could imagine is that scrambling
>> %rdi caused the scheduler to do completely the wrong thing.
>
> I'm questioning the validity, actually. Report says test machine was
> Sandy Bridge-EP and I'd bet good money this one has POPCNT support so
> how are we even hitting that __sw_hweight64() path, at all?
We done 8 tests for the base and 4 tests for the head, and the result is
quite stable.
I found there is another change between the two comments,
base:
"perf-stat.branch-miss-rate": [
0.3089533646503185,
0.3099821038600304,
0.3123762964028104,
0.311511881793534,
0.31231973343587144,
0.3096478429327263,
0.31166037272389924,
0.3097364392684626
],
first bad commit:
"perf-stat.branch-miss-rate": [
0.039853905034485354,
0.0402472142423231,
0.04380682345704418,
0.04319082390667179
],
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.
Best Regards,
Huang, Ying
