----- Original Message ----- > From: "Victor Stinner" <vstinner@xxxxxxxxxx> > To: devel@xxxxxxxxxxxxxxxxxxxxxxx > Sent: Friday, November 15, 2019 10:21:44 AM > Subject: Re: Fedora 32 System-Wide Change proposal: Build Python 3 to statically link with libpython3.8.a for better > performance > > Hi Jan, > > With the helper of Florian Weimer and Charalampos Stratakis, we also agreed > to test this flag in priority. I understood that it disables the LD_PRELOAD > feature: it's no longer possible to override symbols in libpython with > LD_PRELOAD. Thanks to that, the compiler can avoid PLT indirection for > function calls and can inline more function functions in libpython. I'm > talking about a function call from libpython to libpython: something which > is very common in python. Basically, almost all function calls are calls > from libpython to libpython. > > I'm impressed. Thanks to -fno-semantic-interposition, I get the same speedup > on a dynamically linked Python (libpython) compared to statically linked > Python! > > Yesterday, I tried on a vanilla Python compiled manually: > > ./configure --enable-optimizations --with-lto --enable-shared > CFLAGS="-fno-semantic-interposition" LDFLAGS="-fno-semantic-interposition" > > I saw the same speed up than avoiding --enable-shared. Today I validated this > result using the RPM generated by Charalampos's PR: > https://src.fedoraproject.org/rpms/python38/pull-request/53 > > In short, https://fedoraproject.org/wiki/Changes/PythonStaticSpeedup is > useless: there is no need to modify Python to statically link it to > libpython. We can keep the dynamically library libpython and keep Python > dynamically linked to it. We only need to pass -fno-semantic-interposition > to compiler and linker flags when building Python! > > I'm not sure if we need a Fedora change just for a compiler flag. Again, the > only drawback is that we will no longer be able to override a symbol using > LD_PRELOAD. Honestly, I never did that. I don't see any use case for that. > But I used LD_PRELOAD on the libc multiple times to mock the system clock > for example. > > If someone really needs LD_PRELOAD, it's quite easy to build a custom Python > without -fno-semantic-interposition. > > Victor > _______________________________________________ > devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx > To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx > Fedora Code of Conduct: > https://docs.fedoraproject.org/en-US/project/code-of-conduct/ > List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines > List Archives: > https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx > Thanks Victor for running the benchmarks. The change will be withdrawn and another self-contained one will be created. I think not being able to override symbols on the system python is a better tradeoff than the size/speed and possible incompatibilities. Side note: the list of packages that still link to libpython without embedding the interpreter will be used to mass file bugs in order to unlink them. -- Regards, Charalampos Stratakis Software Engineer Python Maintenance Team, Red Hat _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx
