perf pmu: Add perf_pmu__{open,scan}_file_at()

These two helpers will also use openat() to reduce the overhead with
relative pathnames.  Convert other functions in pmu_lookup() to use
the new helpers.

Committer testing:

Before:

  ⬢[acme@toolbox perf-tools-next]$ perf bench internals pmu-scan
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 100 times
    Average PMU scanning took: 2729.040 usec (+- 7.117 usec)
  ⬢[acme@toolbox perf-tools-next]$

After:

  ⬢[acme@toolbox perf-tools-next]$ perf bench internals pmu-scan
  # Running 'internals/pmu-scan' benchmark:
  Computing performance of sysfs PMU event scan for 100 times
    Average PMU scanning took: 2419.870 usec (+- 9.057 usec)
  ⬢[acme@toolbox perf-tools-next]$

Signed-off-by: Namhyung Kim <[email protected]>
Acked-by: Ian Rogers <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Leo Yan <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

0 files changed, 0 insertions, 0 deletions