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trace: Update documentation for mono, mono_raw and boot clock

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

Signed-off-by: Joel Fernandes <joelaf@google.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Link: http://lkml.kernel.org/r/1480372524-15181-8-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Joel Fernandes 2016-11-28 14:35:24 -08:00 committed by Thomas Gleixner
parent 80ec355210
commit 2924ecd441
1 changed files with 20 additions and 0 deletions
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20
Documentation/trace/ftrace.txt
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@ -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, it's 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 in the
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