stream benchmarking on RPi

[Andrew Turner]

On Thu, 5 Sep 2013 14:49:19 -0600
Warner Losh <imp at bsdimp.com> wrote:

> 
> On Sep 5, 2013, at 2:02 PM, Jia-Shiun Li wrote:
> 
> > Hi all,
> > 
> > just did a brief test using stream, the memory bandwidth benchmark,
> > on RPi with Raspbian and FreeBSD. Share these info to see if someone
> > might think of it useful.
> > 
> > FreeBSD is faster at copying. I guess that must be attributed to
> > recent VM and/or superpage commits. I remembered it to be under
> > 300MB/s months before. On the other hand, scale, add, and triad are
> > significantly slower. Anyone have clues or any wild guesses?
> 
> Soft float?

This looks to be the case, stream uses floating point arithmetic for
the scale, add, and triad tests. The copy test is a straight copy from
one array of doubles to another. It looks like most of the speed up in
the copy test is from the move from gcc to clang.

I am planning on investigating moving to softfp on armv6 for 10.1. I
don't expect this to cause any major issues as it is compatible with
the current float ABI in that both pass floating point values in ARM
registers. I think this will improve the test results, but may not be
at the same level as Raspbian appears to use the hard-float ABI. This
is also planned, however I am unsure when this will appear.

Andrew