[aarch64-port-dev ] RFR(s) PPC64/s390x/aarch64: Poor StrictMath performance due to non-optimized compilation (original) (raw)

Gustavo Romero gromero at linux.vnet.ibm.com
Tue Nov 29 16:31:58 UTC 2016

Hi Andrew,

On 29-11-2016 13:35, Andrew Haley wrote:

On 29/11/16 09:41, Volker Simonis wrote:

Thanks Gustavo,

the change looks good. So now we're just waiting for another review from somebody of the aarch64 folks. Once we have that and the fc-request is approved I'll push the changes. One thing I don't understand: cos 0.17098435541865692 1m7.433s 0.1709843554185943 0m56.678s sin 1.7136493465700289 1m10.654s 1.7136493465700542 0m57.114s Do you know what causes the lower digits to be different? Is it that Math and StrictMath use different algorithms, not just different optimization levels?

I don't know exactly what's the root cause for that difference (in the result). The difference is not present on x64, however on PPC64 even with -O0 (as it is by now) that difference exists.

Math methods are intrisified, but StricMath are not. But I understand that Math and StrictMath share the fdlibm code since I already changed some code in fdlibm that reflected both on Math and StrictMath, so it's not clear to me where the Math relaxation occurs on PPC64 (given that such a relaxation is allowed [1]).

For sure others much more experienced than I can comment about difference.

Regards, Gustavo

[1] https://docs.oracle.com/javase/8/docs/api/java/lang/Math.html

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