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

[David Holmes]

Hi Severin,

On 7/09/2018 6:01 PM, Severin Gehwolf wrote:
> 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?

Personally I'd prefer it but I will defer to Erik and Magnus on this.

Thanks,
David

> 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
>>>>>>>
>>>>>>>
>>
>>
>