[PATCH 7/7] trace: Update documentation for mono, mono_raw and boot clock

From: John Stultz
Date: Mon Nov 28 2016 - 17:36:44 EST

From: Joel Fernandes <joelaf@xxxxxxxxxx>

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

Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Richard Cochran <richardcochran@xxxxxxxxx>
Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Joel Fernandes <joelaf@xxxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
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