[Bug c/32523] disastrous scheduling for POWER5

["whaley at cs dot utsa dot edu" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from whaley at cs dot utsa dot edu  2007-06-27 17:00 -------
Andrew,

>PowerPC970FX is not a direct descendent of Power5

Sorry, completely misremembered this.  Since Power4 didn't suffer as bad
as Power5 (I think it lost maybe 10% rather than 50), maybe the 970 will
also not die.

>so I think the case is the register allocator is messing up (which is already known)

OK, can you point me to the bug report?  Is there some way to confirm this
is the problem, rather than the scheduling pass itself?

>The other thing is what options are you using to invoke GCC with?

My Makefile shows them.  The gcc3-derived flags are:
   -mcpu=power5 -mtune=power5 -O3 -m64
for gcc4, I get most of my performance back if I add:
   -fno-schedule-insns -fno-rerun-loop-opt

I include below example output and arch info on the machine I created the
benchmark on (forgot to include it before, sorry).

Thanks,
Clint

r78n04 noibm122/TEST> uname -a
Linux r78n04 2.6.5-7.244-pseries64 #1 SMP Mon Dec 12 18:32:25 UTC 2005 ppc64
ppc64 ppc64 GNU/Linux

r78n04 noibm122/TEST> /usr/bin/gcc -v
Reading specs from /usr/lib/gcc-lib/powerpc-suse-linux/3.3.3/specs
Configured with: ../configure --enable-threads=posix --prefix=/usr
--with-local-prefix=/usr/local --infodir=/usr/share/info
--mandir=/usr/share/man --enable-languages=c,c++,f77,objc,java,ada
--disable-checking --libdir=/usr/lib --enable-libgcj
--with-gxx-include-dir=/usr/include/g++ --with-slibdir=/lib --with-system-zlib
--enable-shared --enable-__cxa_atexit --host=powerpc-suse-linux
--build=powerpc-suse-linux --target=powerpc-suse-linux
--enable-targets=powerpc64-suse-linux --enable-biarch
Thread model: posix
gcc version 3.3.3 (SuSE Linux)

r78n04 noibm122/TEST> gcc -v
Using built-in specs.
Target: powerpc64-unknown-linux-gnu
Configured with: ../configure --prefix=/home/whaley/local/linux
--enable-languages=c --with-gmp=/u/noibm122/local/linux
--with-mpfr-lib=/u/noibm122/local/linux/lib
--with-mpfr-include=/u/noibm122/local/linux/include
Thread model: posix
gcc version 4.2.0

r78n04 TEST/MMBENCH_PPC> make all
/usr/bin/gcc -DREPS=1000 -DWALL -mcpu=power5 -mtune=power5 -O3 -m64 -c
mmbench.c
/usr/bin/gcc -DREPS=1000 -DWALL -mcpu=power5 -mtune=power5 -O3 -m64 -c
dgemm_atlas.c
/usr/bin/gcc -DREPS=1000 -DWALL -mcpu=power5 -mtune=power5 -O3 -m64 -o
xdmm_gcc3 mmbench.o dgemm_atlas.o
rm -f *.o
/u/noibm122/local/linux/home/whaley/local/linux/bin/gcc -DREPS=1000 -DWALL
-mcpu=power5 -mtune=power5 -O3 -m64 -c mmbench.c
/u/noibm122/local/linux/home/whaley/local/linux/bin/gcc -DREPS=1000 -DWALL
-mcpu=power5 -mtune=power5 -O3 -m64 -c dgemm_atlas.c
/u/noibm122/local/linux/home/whaley/local/linux/bin/gcc -DREPS=1000 -DWALL
-mcpu=power5 -mtune=power5 -O3 -m64 -o xdmm_gcc4 mmbench.o dgemm_atlas.o
rm -f *.o
/u/noibm122/local/linux/home/whaley/local/linux/bin/gcc -DREPS=1000 -DWALL
-mcpu=power5 -mtune=power5 -O3 -m64 -c mmbench.c
/u/noibm122/local/linux/home/whaley/local/linux/bin/gcc -DREPS=1000 -DWALL
-mcpu=power5 -mtune=power5 -O3 -m64 -fno-schedule-insns -fno-rerun-loop-opt -c
\
                dgemm_atlas.c
/u/noibm122/local/linux/home/whaley/local/linux/bin/gcc -DREPS=1000 -DWALL
-mcpu=power5 -mtune=power5 -O3 -m64 -o xdmm_gcc4_nosched mmbench.o
dgemm_atlas.o
rm -f *.o
echo "GCC 3.x performance:"
GCC 3.x performance:
./xdmm_gcc3
ALGORITHM     NB   REPS        TIME      MFLOPS
=========  =====  =====  ==========  ==========

atlasmm       40   1000       0.026     4998.24

echo "GCC 4.2 performance:"
GCC 4.2 performance:
./xdmm_gcc4
ALGORITHM     NB   REPS        TIME      MFLOPS
=========  =====  =====  ==========  ==========

atlasmm       40   1000       0.034     3806.35

echo "GCC 4.2 w/o scheduling performance:"
GCC 4.2 w/o scheduling performance:
./xdmm_gcc4_nosched
ALGORITHM     NB   REPS        TIME      MFLOPS
=========  =====  =====  ==========  ==========

atlasmm       40   1000       0.025     5044.53


-- 

whaley at cs dot utsa dot edu changed:

           What    |Removed                     |Added
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          Component|target                      |c


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32523