RFR: 8210416: [linux] Poor StrictMath performance due to non-optimized compilation

[Severin Gehwolf]

Hi,

On Thu, 2018-09-06 at 10:55 -0700, Erik Joelsson wrote:
> On 2018-09-06 10:29, Severin Gehwolf wrote:
> > On Thu, 2018-09-06 at 09:55 -0700, Erik Joelsson wrote:
> > Thanks, Erik. GCC supports -ffp-contract since 4.6. Clang has -ffp-
> > contract too. Question is beginning from which version. That's why I'd
> > expect for those flags to work on linux. Is there anything else I need
> > to check?
> > 
> > Would it be preferred if I moved this into a block like this?
> > 
> > ifeq ($(TOOLCHAIN_TYPE), gcc)
> >    [...]
> > endif
> 
> Yes, making it conditional on toolchain type is what David was after.

Right. David, given that -ffp-contract is available for clang too, do
you still want me to add this into a toolchain specific block?

Also note that solaris doesn't seem to be handling this code any
special, so there would be a difference between gcc + solaris and
solstudio + solaris. Rather hypothetical case, I suppose, but still ;-) 
One of the arguments were that gcc is being used on other platforms
than linux.

> You can also consider adding a capability check if you know that 
> versions of the compiler that should still work don't have the feature.

One clarification: Does a capability check mean doing this at the
configure step or is there a way one has access to toolchain versions
in make files?

Thanks,
Severin

> /Erik
> > Thanks,
> > Severin
> > 
> > > /Erik
> > > > Thanks,
> > > > Severin
> > > > 
> > > > > Thanks,
> > > > > David
> > > > > 
> > > > > On 5/09/2018 11:12 PM, 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[1] 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
> > > > > > 
> > > > > > Thoughts?
> > > > > > 
> > > > > > Thanks,
> > > > > > Severin
> > > > > > 
> > > > > > 
> 
>