RFR: JDK-8246751 Mac OS build settings should use -O3

[Sergey Bylokhov]

On 6/8/20 10:45 am, Magnus Ihse Bursie wrote:
> On 2020-06-08 19:31, Sergey Bylokhov wrote:
>> One of the reasons why -0s was used from the beginning is the performance of the client related libraries, especially java2d.
>> Does anybody run or plan to run performance tests to check that we do not have performance there?
> As Claes say in the bug report, hopefully any potential performance regression will show up in the  general performance testing.
> 
> The idea here is, after all, that we will *increase* performance. :-)

But how did you know that the performance will increase?

> Is there some specific library/behavior/test that you are worried about that should show performance regression when we increase the optimization level?

This -0s mode was selected because it shows best or equal performance and also provides a less size footprint that affects the client/UI code.
I guess at least some graphical tests should be checked for possible performance regressions, like j2dbench.

BTW there is similar discussion in the  "[macos] bring back O2 opt level for unsafe.cpp" on hotspot-dev at .

> 
> /Magnus
>>
>> On 6/8/20 8:55 am, Magnus Ihse Bursie wrote:
>>>  From Jim's bug report:
>>>
>>> "Mac OS X should use -O3 optimization level to be consistent with other platforms and benefit Mac OS X java with the same performance levels as other platforms.
>>>
>>> Mac OS X has used -Os level optimization since management of the platform JDK was handed over from Apple. This level of optimization was Apple's policy, not OpenJDK's. The policy was established in a time when memory was tight (I was there at the time.) Since then other platforms have moved on, making the decision to target speed over disk space. Specifically, using -O3 level optimization.
>>>
>>> I've personally seen 20-30% improvement in performance in C/C++ applications using -O3 over -Os. But, of course, the performance team should verify the affect on the JDK.
>>>
>>> A 11% real time improvement can be seen with a rough HelloWord compile/run."
>>>
>>> I discussed this with Claes, our performance guru, and he agreed that it is low risk enough that we can push this for JDK 15.
>>>
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8246751
>>> WebRev: http://cr.openjdk.java.net/~ihse/JDK-8246751-macos-optimize-O3/webrev.01
>>>
>>> /Magnus
>>
>>
> 


-- 
Best regards, Sergey.