PPC64: Poor StrictMath performance due to non-optimized compilation
joe darcy
joe.darcy at oracle.com
Thu Nov 17 17:35:05 UTC 2016
Hello,
On 11/16/2016 5:45 PM, Gustavo Romero wrote:
> Hi,
>
> Currently, optimization for building fdlibm is disabled, except for the
> "solaris" OS target [1].
The reason for that is because historically the Solaris compilers have
had sufficient discipline and control regarding floating-point semantics
and compiler optimizations to still implement the Java-mandated results
when optimization was enabled. The gcc family of compilers, for example,
has lacked such discipline.
>
> As a consequence on PPC64 (Linux) StrictMath methods like, but not limited to,
> sin(), cos(), and tan() perform verify poor in comparison to the same methods
> in Math class [2]:
If you are doing your work against JDK 9, note that the pow, hypot, and
cbrt fdlibm methods required by StrictMath have been ported to Java
(JDK-8134780: Port fdlibm to Java). I have intentions to port the
remaining methods to Java, but it is unclear whether or not this will
occur for JDK 9.
Methods in the Math class, such as pow, are often intrinsified and use a
different algorithm so a straight performance comparison may not be as
fair or meaningful in those cases.
>
> Math StrictMath
> ========= ==========
> sin 0m29.984s 1m41.184s
> cos 0m30.031s 1m41.200s
> tan 0m31.772s 1m46.976s
> asin 0m4.577s 0m4.543s
> acos 0m4.539s 0m4.525s
> atan 0m12.929s 0m12.896s
> exp 0m1.071s 0m4.570s
> log 0m3.272s 0m14.239s
> log10 0m4.362s 0m20.236s
> sqrt 0m0.913s 0m0.981s
> cbrt 0m10.786s 0m10.808s
> sinh 0m4.438s 0m4.433s
> cosh 0m4.496s 0m4.478s
> tanh 0m3.360s 0m3.353s
> expm1 0m4.076s 0m4.094s
> log1p 0m13.518s 0m13.527s
> IEEEremainder 0m38.803s 0m38.909s
> atan2 0m20.100s 0m20.057s
> pow 0m14.096s 0m19.938s
> hypot 0m5.136s 0m5.122s
>
>
> Switching on the O3 optimization can damage precision of those methods,
> nonetheless it's possible to avoid that side effect and yet get huge benefits of
> the -O3 optimization on PPC64 if -fno-expensive-optimizations is passed in
> addition to the -O3 optimization flag.
>
> In that sense the following change is proposed to resolve the issue:
>
> diff -r 81eb4bd34611 make/lib/CoreLibraries.gmk
> --- a/make/lib/CoreLibraries.gmk Wed Nov 09 13:37:19 2016 +0100
> +++ b/make/lib/CoreLibraries.gmk Wed Nov 16 19:11:11 2016 -0500
> @@ -33,10 +33,16 @@
> # libfdlibm is statically linked with libjava below and not delivered into the
> # product on its own.
>
> -BUILD_LIBFDLIBM_OPTIMIZATION := HIGH
> +BUILD_LIBFDLIBM_OPTIMIZATION := NONE
>
> -ifneq ($(OPENJDK_TARGET_OS), solaris)
> - BUILD_LIBFDLIBM_OPTIMIZATION := NONE
> +ifeq ($(OPENJDK_TARGET_OS), solaris)
> + BUILD_LIBFDLIBM_OPTIMIZATION := HIGH
> +endif
> +
> +ifeq ($(OPENJDK_TARGET_OS), linux)
> + ifeq ($(OPENJDK_TARGET_CPU_ARCH), ppc)
> + BUILD_LIBFDLIBM_OPTIMIZATION := HIGH
> + endif
> endif
>
> LIBFDLIBM_SRC := $(JDK_TOPDIR)/src/java.base/share/native/libfdlibm
> @@ -51,6 +57,7 @@
> CFLAGS := $(CFLAGS_JDKLIB) $(LIBFDLIBM_CFLAGS), \
> CFLAGS_windows_debug := -DLOGGING, \
> CFLAGS_aix := -qfloat=nomaf, \
> + CFLAGS_linux_ppc := -fno-expensive-optimizations, \
> DISABLED_WARNINGS_gcc := sign-compare, \
> DISABLED_WARNINGS_microsoft := 4146 4244 4018, \
> ARFLAGS := $(ARFLAGS), \
>
>
> diff -r 2a1f97c0ad3d make/common/NativeCompilation.gmk
> --- a/make/common/NativeCompilation.gmk Wed Nov 09 15:32:39 2016 +0100
> +++ b/make/common/NativeCompilation.gmk Wed Nov 16 19:08:06 2016 -0500
> @@ -569,16 +569,19 @@
> $1_ALL_OBJS := $$(sort $$($1_EXPECTED_OBJS) $$($1_EXTRA_OBJECT_FILES))
>
> # Pickup extra OPENJDK_TARGET_OS_TYPE and/or OPENJDK_TARGET_OS dependent variables for CFLAGS.
> - $1_EXTRA_CFLAGS:=$$($1_CFLAGS_$(OPENJDK_TARGET_OS_TYPE)) $$($1_CFLAGS_$(OPENJDK_TARGET_OS))
> + $1_EXTRA_CFLAGS:=$$($1_CFLAGS_$(OPENJDK_TARGET_OS_TYPE)) $$($1_CFLAGS_$(OPENJDK_TARGET_OS)) \
> + $$($1_CFLAGS_$(OPENJDK_TARGET_OS)_$(OPENJDK_TARGET_CPU_ARCH))
> ifneq ($(DEBUG_LEVEL),release)
> # Pickup extra debug dependent variables for CFLAGS
> $1_EXTRA_CFLAGS+=$$($1_CFLAGS_debug)
> $1_EXTRA_CFLAGS+=$$($1_CFLAGS_$(OPENJDK_TARGET_OS_TYPE)_debug)
> $1_EXTRA_CFLAGS+=$$($1_CFLAGS_$(OPENJDK_TARGET_OS)_debug)
> + $1_EXTRA_CFLAGS+=$$($1_CFLAGS_$(OPENJDK_TARGET_OS)_$(OPENJDK_TARGET_CPU_ARCH)_debug)
> else
> $1_EXTRA_CFLAGS+=$$($1_CFLAGS_release)
> $1_EXTRA_CFLAGS+=$$($1_CFLAGS_$(OPENJDK_TARGET_OS_TYPE)_release)
> $1_EXTRA_CFLAGS+=$$($1_CFLAGS_$(OPENJDK_TARGET_OS)_release)
> + $1_EXTRA_CFLAGS+=$$($1_CFLAGS_$(OPENJDK_TARGET_OS)_$(OPENJDK_TARGET_CPU_ARCH)_release)
> endif
>
> # Pickup extra OPENJDK_TARGET_OS_TYPE and/or OPENJDK_TARGET_OS dependent variables for CXXFLAGS.
>
>
> After enabling the optimization it's possible to again up to 3x on performance
> regarding the aforementioned methods without losing precision:
>
> StrictMath, original StrictMath, optimized
> ============================ ============================
> sin 1.7136493465700542 1m41.184s 1.7136493465700542 0m33.895s
> cos 0.1709843554185943 1m41.200s 0.1709843554185943 0m33.884s
> tan -5.5500322522995315E7 1m46.976s -5.5500322522995315E7 0m36.461s
> asin NaN 0m4.543s NaN 0m3.175s
> acos NaN 0m4.525s NaN 0m3.211s
> atan 1.5707961389886132E8 0m12.896s 1.5707961389886132E8 0m7.100s
> exp Infinity 0m4.570s Infinity 0m3.187s
> log 1.7420680845245087E9 0m14.239s 1.7420680845245087E9 0m7.170s
> log10 7.565705562087342E8 0m20.236s 7.565705562087342E8 0m9.610s
> sqrt 6.66666671666567E11 0m0.981s 6.66666671666567E11 0m0.948s
> cbrt 3.481191648389617E10 0m10.808s 3.481191648389617E10 0m10.786s
> sinh Infinity 0m4.433s Infinity 0m3.179s
> cosh Infinity 0m4.478s Infinity 0m3.174s
> tanh 9.999999971990079E7 0m3.353s 9.999999971990079E7 0m3.208s
> expm1 Infinity 0m4.094s Infinity 0m3.185s
> log1p 1.7420681029451895E9 0m13.527s 1.7420681029451895E9 0m8.756s
> IEEEremainder 502000.0 0m38.909s 502000.0 0m14.055s
> atan2 1.570453905253704E8 0m20.057s 1.570453905253704E8 0m10.510s
> pow Infinity 0m19.938s Infinity 0m20.204s
> hypot 5.000000099033372E15 0m5.122s 5.000000099033372E15 0m5.130s
>
>
> I believe that as the FC is passed but FEC is not the change can, after the due
> scrutiny and review, be pushed if a special exception approval grants it. Once
> on 9, I'll request the downport to 8.
Accumulating the the results of the functions and comparisons the sums
is not a sufficiently robust way of checking to see if the optimized
versions are indeed equivalent to the non-optimized ones. The
specification of StrictMath requires a particular result for each set of
floating-point arguments and sums get round-away low-order bits that differ.
Running the JDK math library regression tests and corresponding JCK
tests is recommended for work in this area.
Cheers,
-Joe
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