Threads can have many and kernel modules will be represented as a
tree of maps as well.

Ah, and for a perf.data with 146607 samples:

Before:

[root@doppio ~]# perf stat -r 5 perf report > /dev/null

 Performance counter stats for 'perf report' (5 runs):

     699.823680  task-clock-msecs         #      0.991 CPUs    ( +-   0.454% )
             74  context-switches         #      0.000 M/sec   ( +-   1.709% )
              2  CPU-migrations           #      0.000 M/sec   ( +-  17.008% )
          23114  page-faults              #      0.033 M/sec   ( +-   0.000% )
     1381257019  cycles                   #   1973.721 M/sec   ( +-   0.290% )
     1456894438  instructions             #      1.055 IPC     ( +-   0.007% )
       18779818  cache-references         #     26.835 M/sec   ( +-   0.380% )
         641799  cache-misses             #      0.917 M/sec   ( +-   1.200% )

    0.705972729  seconds time elapsed   ( +-   0.501% )

[root@doppio ~]#

After

 Performance counter stats for 'perf report' (5 runs):

     691.261451  task-clock-msecs         #      0.993 CPUs    ( +-   0.307% )
             72  context-switches         #      0.000 M/sec   ( +-   0.829% )
              6  CPU-migrations           #      0.000 M/sec   ( +-  18.409% )
          23127  page-faults              #      0.033 M/sec   ( +-   0.000% )
     1366395876  cycles                   #   1976.670 M/sec   ( +-   0.153% )
     1443136016  instructions             #      1.056 IPC     ( +-   0.012% )
       17956402  cache-references         #     25.976 M/sec   ( +-   0.325% )
         661924  cache-misses             #      0.958 M/sec   ( +-   1.335% )

    0.696127275  seconds time elapsed   ( +-   0.377% )

I.e. we see some speedup too.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
LKML-Reference: <20090928174846.GA3361@ghostprotocols.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>