[tip:perf/core] perf config: Document the PERF_CONFIG environment variable

[tip-bot for Arnaldo Carvalho de Melo]

Commit-ID:  5de9e5fda05b580c036e1fec6e2d8bf78eb2ac9d
Gitweb:     https://git.kernel.org/tip/5de9e5fda05b580c036e1fec6e2d8bf78eb2ac9d
Author:     Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
AuthorDate: Tue, 30 Jul 2019 11:30:37 -0300
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Mon, 12 Aug 2019 16:26:02 -0300

perf config: Document the PERF_CONFIG environment variable

There was a provision for setting this variable, but not the
getenv("PERF_CONFIG") call to set it, as this was fixed in the previous
cset, document that it can be used to ask for using an alternative
.perfconfig file or to disable reading whatever file exists in the
system or home directory, i.e. using:

  export PERF_CONFIG=/dev/null

Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Luis ClÃudio GonÃalves <lclaudio@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Taeung Song <treeze.taeung@xxxxxxxxx>
Link: https://lkml.kernel.org/n/tip-0u4o967hsk7j0o50zp9ctn89@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/Documentation/perf-config.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/perf/Documentation/perf-config.txt b/tools/perf/Documentation/perf-config.txt
index e4aa268d2e38..c599623a1f3d 100644
--- a/tools/perf/Documentation/perf-config.txt
+++ b/tools/perf/Documentation/perf-config.txt
@@ -40,6 +40,10 @@ The '$HOME/.perfconfig' file is used to store a per-user configuration.
 The file '$(sysconfdir)/perfconfig' can be used to
 store a system-wide default configuration.
 
+One an disable reading config files by setting the PERF_CONFIG environment
+variable to /dev/null, or provide an alternate config file by setting that
+variable.
+
 When reading or writing, the values are read from the system and user
 configuration files by default, and options '--system' and '--user'
 can be used to tell the command to read from or write to only that location.