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

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Message-Id: <1556525011-28022-2-git-send-email-feng.tang@intel.com>
Date:   Mon, 29 Apr 2019 16:03:29 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...nel.org>,
        Eric W Biederman <ebiederm@...ssion.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ying Huang <ying.huang@...el.com>, linux-kernel@...r.kernel.org
Cc:     Feng Tang <feng.tang@...el.com>
Subject: [RFC PATCH 1/3] kernel/sysctl: add description for "latencytop"

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

Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Jonathan Corbet <corbet@....net>
Signed-off-by: Feng Tang <feng.tang@...el.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