Re: B-Tree support function number 3 (strxfrm() optimization)

On Thu, Apr 3, 2014 at 12:19 PM, Thom Brown <thom(at)linux(dot)com> wrote:
> Looking good:
>
> -T 100 -n -f sort.sql
>
> Master: 21.670467 / 21.718653 (avg: 21.69456)
> Patch: 66.888756 / 66.888756 (avg: 66.888756)

These were almost exactly the same figures as I saw on my machine.
However, when compiling with certain additional flags -- with
CFLAGS="-O3 -march=native" -- I was able to squeeze more out of this.
My machine has a recent Intel CPU, "Intel(R) Core(TM) i7-3520M". With
these build settings the benchmark then averages about 75.5 tps across
multiple runs, which I'd call a fair additional improvement. I tried
this because I was specifically interested in the results of a memcmp
implementation that uses SIMD. I believe that these flags make
gcc/glibc use a memcmp implementation that takes advantage of SSE
where supported (and various subsequent extensions). Although I didn't
go to the trouble of verifying all this by going through the
disassembly, or instrumenting the code in any way, that is my best
guess as to what actually helped. I don't know how any of that might
be applied to improve matters in the real world, which is why I
haven't dived into this further, but it's worth being aware of.

--
Peter Geoghegan