Re: [PATCH v2 6/7] perf jevents: Switch build to use jevents.py

[John Garry]

On 13/05/2022 16:58, Ian Rogers wrote:
> On Fri, May 13, 2022 at 8:38 AM John Garry <john.garry@xxxxxxxxxx> wrote:
> > On 11/05/2022 22:15, Ian Rogers wrote:
> > >     # jevents.py uses os.scandir and type hints present in Python 3.5 released in Sept. 2015.
> > > +    JEVENTS_PYTHON_GOOD := $(shell $(PYTHON) -c 'import sys;print("1" if(sys.version_info.major >= 3 and sys.version_info.minor >= 5) else "0")')
> >
> > I think that many - like me - will have python 2.7, so now will find no
> > pmu-events generated any longer after missing this message in the build :(
> >
> > Maybe many will have python >= 3.5 - but I don't know...
>
> So Python 2 has been end-of-life for over 2 years now:
> https://www.python.org/doc/sunset-python-2/
> There have been a number of LKML patches upgrading python to version 3.
>
> Python 3.5 has some very nice features of os.scandir and type hints,
> so if I set the bar lower than this it hurts the code quality. It is
> also at least 6 years old at this point, and so hopefully not
> unreasonable for a distribution to have picked it up :-) Looking at
> the change to C11 thread:
> https://lore.kernel.org/lkml/20220228103142.3301082-1-arnd@xxxxxxxxxx/
> It seems the motivation for picking a language version is the features
> it provides and compatibility. If we choose pre-Python 3.5 we get more
> compatibility but we lose language features.
>
> My feeling is that we shouldn't need to support things that are no
> longer maintained (like Python 2) but I'm less clear if Python 3.5 is
> sufficiently compatible for everyone's needs. I kind of hope so, hence
> making the patches this way.

Fine, I just think that you need to make this transition as seamless as 
possible, otherwise it can be judged as a regression.

For example, I have now python 3.6 (default) and 2.7 but it still 
doesn't seem to work:

john@localhost:~/acme/tools/perf> make
  BUILD:   Doing 'make -j4' parallel build
Warning: Kernel ABI header at 'tools/include/linux/coresight-pmu.h' 
differs from latest version at 'include/linux/coresight-pmu.h'
diff -u tools/include/linux/coresight-pmu.h include/linux/coresight-pmu.h
Makefile.config:593: No sys/sdt.h found, no SDT events are defined, 
please install systemtap-sdt-devel or systemtap-sdt-dev
Makefile.config:871: Python interpreter too old (older than 3.5) 
disabling jevent generation
Makefile.config:904: Old version of libbfd/binutils things like PE 
executable profiling will not be available
Makefile.config:1092: No openjdk development package found, please 
install JDK package, e.g. openjdk-8-jdk, java-1.8.0-openjdk-devel

Auto-detecting system features:
...                         dwarf: [ on  ]
...            dwarf_getlocations: [ on  ]
...                         glibc: [ on  ]
...                        libbfd: [ OFF ]
...                libbfd-buildid: [ OFF ]
...                        libcap: [ on  ]
...                        libelf: [ on  ]
...                       libnuma: [ on  ]
...        numa_num_possible_cpus: [ on  ]
...                       libperl: [ on  ]
...                     libpython: [ on  ]
...                     libcrypto: [ on  ]
...                     libunwind: [ on  ]
...            libdw-dwarf-unwind: [ on  ]
...                          zlib: [ on  ]
...                          lzma: [ on  ]
...                     get_cpuid: [ on  ]
...                           bpf: [ on  ]
...                        libaio: [ on  ]
...                       libzstd: [ on  ]
...        disassembler-four-args: [ on  ]


make[3]: Nothing to be done for 'install_headers'.
john@localhost:~/acme/tools/perf> python --version
Python 3.6.12
john@localhost:~/acme/tools/perf>

which I need to figure out...

> >   > + ifneq ($(JEVENTS_PYTHON_GOOD), 1)
> >   > + $(warning Python interpreter too old (older than 3.5) disabling
> > jevent generation)
> >   > + NO_JEVENTS := 1
> >
> > It is possible to flip NO_JEVENTS to be JEVENTS, i.e. no
> > double-negatives, like NO_JEVENTS := 0
>
> Agreed that double negatives are bad. The NO_... pattern is kind of
> throughout the make files and build files. I preferred the NO_... for
> consistency but if there's a consensus I'm happy to change.

I have no strong preference. I just find that double negatives boggle 
the mind.

Thanks,
john