[RFC PATCH 1/3] kernel/sysctl: add description for "latencytop"

[Feng Tang <feng.tang@intel.com>]

The body of description is mostly copied from comments in
kernel/latencytop.c

Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Feng Tang <feng.tang@intel.com>
---
 Documentation/sysctl/kernel.txt | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index c0527d8..080ef66 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -43,6 +43,7 @@ show up in /proc/sys/kernel:
 - hyperv_record_panic_msg
 - kexec_load_disabled
 - kptr_restrict
+- latencytop
 - l2cr                        [ PPC only ]
 - modprobe                    ==> Documentation/debugging-modules.txt
 - modules_disabled
@@ -437,6 +438,23 @@ When kptr_restrict is set to (2), kernel pointers printed using
 
 ==============================================================
 
+latencytop:
+
+This value controls whether to start collecting kernel latency
+data, it is off (0) by default, and could be switched on (1).
+The latency talked here is not the 'traditional' interrupt
+latency (which is primarily caused by something else consuming CPU),
+but instead, it is the latency an application encounters because
+the kernel sleeps on its behalf for various reasons.
+
+The info is exported via /proc/latency_stats and /proc/<pid>/latency.
+
+This file shows up only if CONFIG_LATENCYTOP is enabled, and please
+be noted that turning it on may bring notable sytstem overhead when
+there are massive scheduling in system.
+
+==============================================================
+
 l2cr: (PPC only)
 
 This flag controls the L2 cache of G3 processor boards. If
-- 
2.7.4