perf stat: Add --log-fd <N> option to redirect stderr elsewhere

This perf stat option emulates valgrind's --log-fd option, allowing the
user to send perf results elsewhere, and leaving stderr for use by the
program under test.  This complements --output file option, and is
mutually exclusive with it.

   3>results  perf stat --log-fd 3          -- $cmd
   3>>results perf stat --log-fd 3 --append -- $cmd

The perl distro's make test.valgrind target uses valgrind's --log-fd
option, I've adapted it to invoke perf also, and tested this patch
there.

Link: http://lkml.kernel.org/r/1315437244-3788-2-git-send-email-jim.cromie@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt
index 08394c4879a8..8966b9ab2014 100644
--- a/tools/perf/Documentation/perf-stat.txt
+++ b/tools/perf/Documentation/perf-stat.txt
@@ -95,12 +95,21 @@ corresponding events, i.e., they always refer to events defined earlier on the c
 line.
 
 -o file::
--output file::
+--output file::
 Print the output into the designated file.
 
 --append::
 Append to the output file designated with the -o option. Ignored if -o is not specified.
 
+--log-fd::
+
+Log output to fd, instead of stderr.  Complementary to --output, and mutually exclusive
+with it.  --append may be used here.  Examples:
+     3>results  perf stat --log-fd 3          -- $cmd
+     3>>results perf stat --log-fd 3 --append -- $cmd
+
+
+
 EXAMPLES
 --------