perf bench numa: Make no args mean 'run all tests'

If we call just:

  perf bench numa mem

it will present the same output as:

  perf bench numa mem -h

i.e. ask for instructions about what to run.

While that is kinda ok, using 'run all tests' as the default, i.e.
making 'no parms' be equivalent to:

  perf bench numa mem -a

Will allow:

  perf bench numa all

to actually do what is asked: i.e. run all the 'bench' tests, instead of
responding to that by asking what to do.

That, in turn, allows:

  perf bench all

to actually complete, for the same reasons.

And after that, the tests that come after that, and that at some point
hit a NULL deref, will run, allowing me to reproduce a recently reported
problem.

That when you have the needed numa libraries, which wasn't the case for
the reporter, making me a bit confused after trying to reproduce his
report.

So make no parms mean -a.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Patrick Palka <patrick@parcs.ath.cx>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-x7h0ghx4pef4n0brywg21krk@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
perf bench: Fix NULL pointer dereference in "perf bench all"

The for_each_bench() macro must check that the "benchmarks" field of a
collection is not NULL before dereferencing it because the "all"
collection in particular has a NULL "benchmarks" field (signifying that
it has no benchmarks to iterate over).

This fixes this NULL pointer dereference when running "perf bench all":

  [root@ssdandy ~]# perf bench all
  <SNIP>

  # Running mem/memset benchmark...
  # Copying 1MB Bytes ...

         2.453675 GB/Sec
        12.056327 GB/Sec (with prefault)

  Segmentation fault (core dumped)
  [root@ssdandy ~]#

Signed-off-by: Patrick Palka <patrick@parcs.ath.cx>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1394664051-6037-1-git-send-email-patrick@parcs.ath.cx
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>