RFR: 8210416: [linux] Poor StrictMath performance due to non-optimized compilation
sgehwolf at redhat.com
Thu Sep 6 10:21:18 UTC 2018
On Wed, 2018-09-05 at 12:15 -0700, joe darcy wrote:
> On 9/5/2018 6:12 AM, Severin Gehwolf wrote:
> > Hi,
> > Cross-posting this review-thread on core-libs-dev and build-dev as
> > this
> > is a build change, but affects fdlibm which is core-libs.
> > With JDK-8170153 optimization for fdlibm code has been turned on
> > for
> > ppc64 s390 and aarch64. This patch intends to turn it on on all
> > arches
> > on Linux. I've not observed any precision issues. Is there a good
> > reason to not use -O3 -ffp-contract=off everywhere?
> > Bug: https://bugs.openjdk.java.net/browse/JDK-8210416
> > webrev:
> > http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8210416/webrev.01/
> > Testing: - java/lang/Math, java/lang/StrictMath tests (all pass).
> > - Currently running through submit repo.
> > A simple micro benchmark from JDK-8170153 shows these numbers
> > for
> > StrictMath:
> > Function | before | after
> > ----------------------------------------------
> > sin | 0m33.382s | 0m18.731s
> > cos | 0m31.562s | 0m18.796s
> > tan | 0m33.657s | 0m21.093s
> > atan | 0m5.714s | 0m4.902s
> > log | 0m6.212s | 0m4.439s
> > log10 | 0m7.946s | 0m5.543s
> > sqrt | 0m0.481s | 0m0.449s
> > cbrt | 0m5.295s | 0m5.214s
> > tanh | 0m1.404s | 0m1.307s
> > log1p | 0m6.457s | 0m5.131s
> > IEEEremainder | 0m10.629s | 0m6.048s
> > atan2 | 0m8.037s | 0m5.668s
> > hypot | 0m2.171s | 0m2.147s
> Note that pow (JDK-8134795), hypot (JDK-7130085), cbrt (JDK-8136799),
> and exp (JDK-8139688), have been ported to Java as of JDK 9. The sqrt
> method is commonly handled as an intrinsic.
OK thanks. Since ppc64/s390x/aarch64 uses this already on Linux do you
anticipate the same being applied to x86/x86_64 causing issues (modulo
compiler bugs of course)?
> Testing that was not geared toward finding precision/rounding issues
> would be unlikely to find them.
Would running the TCK be geared towards precision/rounding issues? I
could ask someone to run the TCK on a test build on x86_64/x86 to find
> I don't see the sources of the microbenchmark in JDK-8170153.
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