linux-kernel - [PATCH 7/7] trace: Update documentation for mono, mono

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Date:   Mon, 28 Nov 2016 14:35:24 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     lkml <linux-kernel@...r.kernel.org>
Cc:     Joel Fernandes <joelaf@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Richard Cochran <richardcochran@...il.com>,
        Prarit Bhargava <prarit@...hat.com>,
        John Stultz <john.stultz@...aro.org>
Subject: [PATCH 7/7] trace: Update documentation for mono, mono_raw and boot clock

From: Joel Fernandes <joelaf@...gle.com>

Documentation was missing for mono and mono_raw, add them and also for
the boot clock introduced in this series.

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Richard Cochran <richardcochran@...il.com>
Cc: Prarit Bhargava <prarit@...hat.com>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Joel Fernandes <joelaf@...gle.com>
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
 Documentation/trace/ftrace.txt | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index 185c39f..5180b09 100644
--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -362,6 +362,26 @@ of ftrace. Here is a list of some of the key files:
 		  to correlate events across hypervisor/guest if
 		  tb_offset is known.
 
+	  mono: This uses the fast monotonic clock (CLOCK_MONOTONIC)
+		which is monotonic and is subject to NTP rate adjustments.
+
+	  mono_raw:
+		This is the raw monotonic clock (CLOCK_MONOTONIC_RAW)
+		which is montonic but is not subject to any rate adjustments
+		and ticks at the same rate as the hardware clocksource.
+
+	  boot: This is the boot clock (CLOCK_BOOTTIME) and is based on the
+		fast monotonic clock, but also accounts for time spent in
+		suspend. Since the clock access is designed for use in
+		tracing in the suspend path, some side effects are possible
+		if clock is accessed after the suspend time is accounted before
+		the fast mono clock is updated. In this case, the clock update
+		appears to happen slightly sooner than it normally would have.
+		Also on 32-bit systems, its possible that the 64-bit boot offset
+		sees a partial update. These effects are rare and post
+		processing should be able to handle them. See comments on
+		ktime_get_boot_fast_ns function for more information.
+
 	To set a clock, simply echo the clock name into this file.
 
 	  echo global > trace_clock
-- 
2.7.4