On Tue, Feb 7, 2017 at 7:50 AM, Bharat Bhushan
<bharat.bhushan@linaro.org> wrote:
> I am working on log10/qsort benchmarks on ARM64 (ARMv8) processor,
> I want to check if we have experience with these benchmarks.

We have experience with things like SPEC and Coremark, which are
compiler performance benchmarks.  log10/qsort sounds like glibc
functions.  Are you testing glibc performance?  That would perhaps
depend more on the glibc version than the compiler version.

> Actually i am looking for a compiler version which gives best results with
> these benchmarks and specific compiler optimization (in my case is see O3
> gives best numbers) ?

What exactly are you trying to optimize?  If you want best performance
for your application, then you try every compiler version and every
option and use the combination that gives the best performance.  Us
toolchain developers only care about performance of the latest
version, and if it isn't the best performing one, then we try to fix
it.  If you want best performance for the most people, then you
concentrate on -O2 results as that is what most people use.  I can't
give a better answer without more specifics of what exactly you are
trying to do.

> I have tried GCC-4.9 and GCC-6.2 with log10 benchmark and my observations
> are:
> 1)      With gcc 4.9    -   140 us
>             2)      With GCC 6.2   -   150 us
> My compilation flags are "-O3 -ftree-vectorize -funroll-all-loops --param
> max-inline-insns-auto=550 --param case-values-threshold=30
> -falign-functions=32 -ftracer"
>
> So it seems like gcc-6.2 is better, am i missing something, should i use
> some better compiler flags?

Usually for benchmarks, a faster runtime is a better result, so it
looks like gcc-4.9 is giving the better result.  If that is a gcc-6
bug, then it should be reported so we can try to fix it.  However, you
are using a lot of options, and some of those options aren't the
default because they don't always give the best results.  The
usefulness of some uncommon optimization options can vary from one gcc
release to the next.  You may need to use different sets of gcc
options with different gcc versions to get the best results.  But
again, as mentioned above, this all depends on what exactly you are
trying to do, and you haven't given us enough info to understand that.

Jim