We should also be wary of compiler options that are a win on one
processor family and a loss on another. Anything that schedules
instructions may be specific to a particular generation of CPUs, for
instance. Or for i5 vs i7 vs M(obile)...
...jim
On 10/2/15 9:10 AM, Laurent Bourgès wrote:
Sergey,
thanks for the information:
I tried your gcc options on my ubuntu 14.4 (v4.8.4) and it is
actually
slightly faster: 10% on my fill ellipse test (450ms vs 490ms).
I tested by your jmh test, and the difference became bigger on 1400
size.
Interesting; I will try too.
Do you know which gcc compiler and options are used to build
JavaSE EA?
I guess that compiler options in makefile are the same.
plus some default gcc options:
jdk8:
gcc (GCC) 4.3.0 20080428 (Red Hat-8) C compiler version 4.3.0-8)
jdk9:
gcc-4.8.2 - OEL5.5
However the gcc compiler are different: 4.3 vs 4.8.2 !
So it may be worth comparing their different optimization options; I
guess somebody already looked at that !
Moreover, the linux distrib may define default options.
I will try to figure out all compiler options (command line +
defaults)
on my machine.
It is not simple to find an option, which will help for everyone.
Two options suggested by me is a minimum number from -O3 to get the
maximum performance, both seems reasonable. Actually if I change the
-O2 to -O3(OPTIMIZATION := LOW =>> OPTIMIZATION := HIGHEST)
performance became worse.
It is often the case with O3, but your patch seems a good win with only
2 enabled options.
What is your build environment ?
Ubuntu 14.04 gcc 4.8.4
I have the same and I got finally my gcc options:
gcc -c -Q -O2 --help=common
Here are the difference between O2 vs O3 with gcc 4.8.4:
gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
diff /tmp/O2-opts /tmp/O3-opts | grep enabled
*> -fgcse-after-reload [enabled]
*> -finline-functions [enabled]
-fipa-cp-clone [enabled]
-fpredictive-commoning [enabled]
-ftree-loop-distribute-patterns [enabled]
-ftree-partial-pre [enabled]
*> -ftree-vectorize [enabled]
*> -funswitch-loops [enabled]
-fvect-cost-model [enabled]
So we could evaluate some of these options and see what is the best
compromise for libawt on gcc 4.8 !
Regards,
Laurent
