svn commit: r281103 - head/sys/amd64/amd64

[Bruce Evans]

On Mon, 6 Apr 2015, Adrian Chadd wrote:

> Hi Bruce,
>
> There's been a bunch of research into that field lately.
>
> Eg: http://daim.idi.ntnu.no/masteroppgaver/009/9231/masteroppgave.pdf
>
> The best part (imho)- the length of your USER environment string
> influencing code runtime costs. :)

I fix the latter in an FP benchmark by aligning the stack to a page
boundary, and further adjusting it by a magic amount of a few hundred.
This only works for microbenchmarks, since in general the stack pointer
is too variable for a single adjustment to keep it from hitting things.

Bruce