Re: Getting the latest and greatest Linux perf features on every Debian kernel

[Ian Rogers <irogers@google.com>]

So I wanted to say a BIG thanks to Ben as I see in the 5.16 changelog
that the perf wrapper script for Debian is now gone!
https://metadata.ftp-master.debian.org/changelogs//main/l/linux/linux_6.1~rc8-1~exp1_changelog

```
linux (5.16.3-1~exp1) experimental; urgency=medium
...
  * linux-perf: Build a single unversioned package of perf, as it is no
    longer necessary to match the kernel version
```

I notice from trying the experimental version the features are:
```
perf version 6.1.0-rc8
                dwarf: [ on  ]  # HAVE_DWARF_SUPPORT
   dwarf_getlocations: [ on  ]  # HAVE_DWARF_GETLOCATIONS_SUPPORT
                glibc: [ on  ]  # HAVE_GLIBC_SUPPORT
        syscall_table: [ on  ]  # HAVE_SYSCALL_TABLE_SUPPORT
               libbfd: [ OFF ]  # HAVE_LIBBFD_SUPPORT
           debuginfod: [ OFF ]  # HAVE_DEBUGINFOD_SUPPORT
               libelf: [ on  ]  # HAVE_LIBELF_SUPPORT
              libnuma: [ on  ]  # HAVE_LIBNUMA_SUPPORT
numa_num_possible_cpus: [ on  ]  # HAVE_LIBNUMA_SUPPORT
              libperl: [ on  ]  # HAVE_LIBPERL_SUPPORT
            libpython: [ on  ]  # HAVE_LIBPYTHON_SUPPORT
             libslang: [ on  ]  # HAVE_SLANG_SUPPORT
            libcrypto: [ OFF ]  # HAVE_LIBCRYPTO_SUPPORT
            libunwind: [ on  ]  # HAVE_LIBUNWIND_SUPPORT
   libdw-dwarf-unwind: [ on  ]  # HAVE_DWARF_SUPPORT
                 zlib: [ on  ]  # HAVE_ZLIB_SUPPORT
                 lzma: [ on  ]  # HAVE_LZMA_SUPPORT
            get_cpuid: [ on  ]  # HAVE_AUXTRACE_SUPPORT
                  bpf: [ on  ]  # HAVE_LIBBPF_SUPPORT
                  aio: [ on  ]  # HAVE_AIO_SUPPORT
                 zstd: [ OFF ]  # HAVE_ZSTD_SUPPORT
              libpfm4: [ OFF ]  # HAVE_LIBPFM
```
I believe this is a step up as previously libpython was disabled.

I had a few things to ask wrt this thread and getting the best
possible Debian experience:
 - in Linux 6.2 the libtraceevent will need to become an external
library dependency

 - are there issues with debuginfod/zstd enablement? libbfd has
licensing issues. libcrypto is only used by the JIT support, but still
may be nice to enable.

- wrt packaging, the kernel has a deb-pkg build target, should we move
the debian packaging to something like a perf-deb-pkg similar to the
perf-tar-src-pkg target? This thread was previously proposing using
the source releases Arnaldo makes, this would be possible for a
deb-pkg target if the logic were contained in the source tar ball. I
believe what is currently being built is from a kernel tree, but
perhaps a build target adds consistency with the kernel, allows
contributors to update the Debian related files and serves as an
example for similar packaging of other kernel tools, like bpftool.

 - are there some residual wrapper artifacts in the package, for example:
```
$ dpkg -L linux-perf
/.
/usr
/usr/bin
/usr/bin/perf
package diverts others to: /usr/bin/perf.wrapper
...
package diverts others to: /usr/share/bash-completion/completions/perf.wrapper
...
package diverts others to: /usr/share/man/man1/perf.wrapper.1.gz
...
```

Another BIG thank you to Ben!

Ian