On Wed, 26 Feb 2025 13:24:57 GMT, Matthias Baesken <mbaes...@openjdk.org> wrote:
>> I think it might be worth trying to take a more structured approach to the
>> optimizations used. Maybe setup a wiki page with all native libraries, what
>> current optimization levels they use, and what the difference in size would
>> be for e.g. SIZE and HIGH instead. Ideally, we would also have some kind of
>> microbenchmark associated with each library that could say anything about
>> the performance of the library, but that is probably not realistic in most
>> cases. But I guess that people familiar with the library can make some
>> educated guess about the performance sensitivity of the libraries, and what
>> would stress them.
>>
>> Furthermore, I think we can definitely consider changes in the build system
>> to support some of the requests that have arisen here, like allowing JDK
>> libraries (apart from Hotspot) to allow LTO, or to have a way to override
>> optimization levels for JDK libraries from the configure command line,
>> similar to the JVM feature `opt-size`.
>>
>> I am also open to reconsidering the entire idea of "optimization levels" the
>> way it is currently implemented. Developers tend to think in terms of `-O2`,
>> and our named optimization levels just inserts an extra layer of uncertainty
>> ("what does `HIGHEST` really mean?). A problem is of course that different
>> compilers have different ways of expressing optimization (most clearly how
>> the Microsoft VS compiler differs from gcc/clang), but then again, maybe
>> that just means that we should express this as:
>>
>>
>> OPT_gcc_clang := -O1, \
>> OPT_microsoft := -O2. \
>>
>>
>> since it is not obvious that there really is a good way to package different
>> optimization flags for different compilers that make sense for all
>> libraries. Our current code assumes this is the case, but this does not
>> necessarily have to be true.
>
>> Maybe setup a wiki page with all native libraries, what current
>> optimization levels they use, and what the difference in size would be for
>> e.g. SIZE and HIGH instead.
>
> Hi @magicus I can collect some info from our builds (gcc13, xlc17, Xcode15,
> VS2022).
> Should we place the wiki here ? https://wiki.openjdk.org/display/Build
> Seems I can edit the pages there but not create a new one , can you !?
> @MBaesken I don't know why you could not add new pages (everyone in the Build
> Group should be able to do that). The UI is a bit strange, I usually create a
> new page by creating a tentative link from an existing one.
>
> Anyway, I created
> https://wiki.openjdk.org/display/Build/Native+library+optimization+level+research.
> It's all yours!
Thanks ! I'll most likely have some time next week to collect and add some info
from our build envs we use at SAP.
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PR Comment: https://git.openjdk.org/jdk/pull/23563#issuecomment-2690369940
