[tip:perf/core] perf docs: Add description for stderr

[tip-bot for Thomas Richter <tipbot@zytor.com>]

Commit-ID:  6cf626563998d3f8770cc25146986810ee4a5969
Gitweb:     https://git.kernel.org/tip/6cf626563998d3f8770cc25146986810ee4a5969
Author:     Thomas Richter <tmricht@linux.ibm.com>
AuthorDate: Mon, 13 May 2019 10:02:20 +0200
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Thu, 16 May 2019 14:17:24 -0300

perf docs: Add description for stderr

'perf report' displays recorded data on the screen and emits warnings
and debug messages in the status line (last one on screen).

perf also supports the possibility to write all debug messages to stderr
(instead of writing them to the status line).

This is achieved with the following command:

  # ./perf --debug stderr=1 report -vvvvv -i ~/fast.data 2>/tmp/2
  # ll /tmp/2
  -rw-rw-r-- 1 tmricht tmricht 5420835 May  7 13:46 /tmp/2
  #

The usage of variable stderr=1 is not documented, so add it to the perf
man page.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: http://lkml.kernel.org/r/20190513080220.91966-1-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/Documentation/perf.txt | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/perf/Documentation/perf.txt b/tools/perf/Documentation/perf.txt
index 864e37597252..401f0ed67439 100644
--- a/tools/perf/Documentation/perf.txt
+++ b/tools/perf/Documentation/perf.txt
@@ -22,6 +22,8 @@ OPTIONS
 	  verbose          - general debug messages
 	  ordered-events   - ordered events object debug messages
 	  data-convert     - data convert command debug messages
+	  stderr           - write debug output (option -v) to stderr
+	                     in browser mode
 
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 	Setup buildid cache directory. It has higher priority than