Perfromance Test Results using gcc-linaro-4.5-2010.11-1

[Michael Hope]

On Wed, Dec 8, 2010 at 7:10 PM, Michael Hope <michael.hope at linaro.org> wrote:
> On Wed, Dec 8, 2010 at 6:59 PM, Prashanth S <prashanth.s at samsung.com> wrote:
>>
>> Dear All
>>
>>     Our team in Samsung collected some performance metrics for the following
>> 3 GCC cross compilers
>>
>> Gentoo Complier(part of Chrome OS Build Environment)
>> GCC 4.4.1 (Code Sourcery).
>> Linaro (gcc-linaro-4.5-2010.11-1)
>>
>> Flags used to Build Linaro Tool chain
>>        used Michael Hope Script .Just modified "GCCFLAGS = --with-mode=thumb
>> --with-arch=armv7-a --with-float=softfp --with-fpu=neon
>> --with-fpu=vfpv3-d16"

Some notes on the flags themselves:

The options in your email are quite decent:
 -mtune=cortex-a9 -mfloat-abi=softfp -mfpu=neon -ftree-vectorize
-fomit-frame-pointer -ffast-math -mcpu=cortex-a9   -O3

You can prune that back a bit to:
  -mcpu=cortex-a9 -mfloat-abi=softfp -mfpu=neon -ffast-math -O3

as -O turns on -fomit-frame-pointer, -O3 turns on -ftree-vectorize,
and -mcpu implies -mtune.

You can prune this back even further by configuring and building the
compiler using --with-cpu and similar options.  These set the defaults
so you can use just:
  -ffast-math -O3

Be careful with -ffast-math.  It will improve performance but means
that floating point calculations no longer follow the full IEEE 754
standard.  I'd turn this off until you verify individual packages.

-mfloat-abi=hard will give better performance but may involve a porting effort.

-fno-common also gives a small improvement in various benchmarks, but
may break some programs.

Note that the 'best' options depend on the individual program.  It's
not unusual for programs to sometimes do better with -O2 than -O3, or
better without -ftree-vectorise.  I'd be interested in any situations
you run across.

-- Michael