When building tools/lib/bpf as part of the tools/perf/ build process,
which will happend when we introduce a patch wiring that up, we end up
stomping on the feature detection caching mechanism, that uses a file in
the output directory (O=) that is shared by libbpf and perf to check if
something changed from one build to another that requires redoing the
feature detection process.
By using the recently introduced FEATURE_USER tools/build/ knob, we can
avoid that:
Before, every make invokation would run the feature detection:
$ make O=/tmp/build/perf -C tools/perf
make: Entering directory '/home/git/linux/tools/perf'
Auto-detecting system features:
... dwarf: [ on ]
... glibc: [ on ]
<SNIP>
... get_cpuid: [ on ]
... bpf: [ on ]
GEN perf-archive
GEN perf-with-kcore
Auto-detecting system features:
... libelf: [ on ]
... bpf: [ on ]
<SNIP>
After:
$ make O=/tmp/build/perf -C tools/perf
make: Entering directory '/home/git/linux/tools/perf'
BUILD: Doing 'make -j4' parallel build
make: Leaving directory '/home/git/linux/tools/perf'
$
Because we now have two different feature detection state files:
$ ls -la /tmp/build/perf/FEATURE-DUMP*
-rw-rw-r--. 1 acme acme 338 Sep 21 17:25 /tmp/build/perf/FEATURE-DUMP
-rw-rw-r--. 1 acme acme 33 Sep 21 17:25 /tmp/build/perf/FEATURE-DUMP.libbpf
$
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: pi3orama@163.com
Fixes: 1b76c13e4b ("bpf tools: Introduce 'bpf' library and add bpf feature check")
Link: http://lkml.kernel.org/n/tip-s6ev9wfqy7pvvs58emys2g90@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
65f041bee7