perf top: Add processing thread

Add a new thread that takes care of the hist creating to alleviate the
main reader thread so it can keep perf mmaps served in time so that we
reduce the possibility of losing events.

The 'perf top' command now spawns 2 extra threads, the data processing
is the following:

  1) The main thread reads the data from mmaps and queues them to
     ordered events object;

  2) The processing threads takes the data from the ordered events
     object and create initial histogram;

  3) The GUI thread periodically sorts the initial histogram and
     presents it.

Passing the data between threads 1 and 2 is done by having 2 ordered
events queues. One is always being stored by thread 1 while the other is
flushed out in thread 2.

Passing the data between threads 2 and 3 stays the same as was initially
for threads 1 and 3.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-hhf4hllgkmle9wl1aly1jli0@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>