Before:

[acme@emilia ~]$ perf record -o perf_report.perf perf stat perf report > /dev/null

 Performance counter stats for 'perf':

     245.414985  task clock ticks     (msecs)
              6  context switches     (events)
              6  CPU migrations       (events)
           2108  pagefaults           (events)
       37493013  CPU cycles           (events)  (scaled from 67.04%)
       13576789  instructions         (events)  (scaled from 66.76%)
          57931  cache references     (events)  (scaled from 21.96%)
          12263  cache misses         (events)  (scaled from 21.98%)

 Wall-clock time elapsed:   246.575587 msecs

[acme@emilia ~]$ perf report -i perf_report.perf | head
12.15          perf [.] 0x000000000005432a /lib64/libc-2.5.so: _IO_vfscanf_internal
 9.38          perf [k] 0xffffffff8101b1d2 intel_pmu_enable_all
 8.53          perf [.] 0x00000000000056b8 /home/acme/git/linux-2.6-tip/Documentation/perf_counter/perf: dso__insert_symbol
 6.61          perf [.] 0x00000000000057cb /home/acme/git/linux-2.6-tip/Documentation/perf_counter/perf: dso__find_symbol
 5.33          perf [k] 0xffffffff811ce082 number
 4.69          perf [.] 0x0000000000034829 /lib64/libc-2.5.so: ____strtoull_l_internal
 4.48          perf [.] 0x0000000000006505 /home/acme/git/linux-2.6-tip/Documentation/perf_counter/perf: thread__symbol_incnew
 3.41          perf [.] 0x000000000000fce6 /home/acme/git/linux-2.6-tip/Documentation/perf_counter/perf: rb_insert_color
 3.20          perf [k] 0xffffffff811cfc01 vsnprintf
 2.99          perf [k] 0xffffffff811ce5e8 format_decode

After:

[acme@emilia ~]$ perf record -o perf_report.perf perf stat perf report > /dev/null

 Performance counter stats for 'perf':

     218.186805  task clock ticks     (msecs)
              4  context switches     (events)
              7  CPU migrations       (events)
           2133  pagefaults           (events)
       32735365  CPU cycles           (events)  (scaled from 67.04%)
       11952309  instructions         (events)  (scaled from 66.26%)
          50314  cache references     (events)  (scaled from 21.96%)
          13228  cache misses         (events)  (scaled from 21.98%)

 Wall-clock time elapsed:   218.810451 msecs

[acme@emilia ~]$ perf report -i perf_report.perf | head
10.68          perf [.] 0x000000000000578d /home/acme/git/linux-2.6-tip/Documentation/perf_counter/perf: dso__find_symbol
 9.62          perf [.] 0x00000000000065f7 /home/acme/git/linux-2.6-tip/Documentation/perf_counter/perf: thread__symbol_incnew
 9.40          perf [.] 0x00000000000056b4 /home/acme/git/linux-2.6-tip/Documentation/perf_counter/perf: dso__insert_symbol
 9.19          perf [k] 0xffffffff8101b1d2 intel_pmu_enable_all
 5.13          perf [.] 0x0000000000005ec7 /home/acme/git/linux-2.6-tip/Documentation/perf_counter/perf: hex2long
 4.49          perf [k] 0xffffffff81083808 kallsyms_expand_symbol
 3.85          perf [k] 0xffffffff811ce2c1 number
 3.63          perf [.] 0x0000000000005e81 /home/acme/git/linux-2.6-tip/Documentation/perf_counter/perf: hex
 2.99          perf [.] 0x000000000000fd5b /home/acme/git/linux-2.6-tip/Documentation/perf_counter/perf: rb_insert_color
 2.99          perf [k] 0xffffffff811cf251 string
[acme@emilia ~]$

[ Impact: optimization ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Kacur <jkacur@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20090526222057.GI4424@ghostprotocols.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>