trace: Update documentation for mono, mono_raw and boot clock

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>

diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index 185c39f..5596e2d 100644 (file)
--- 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, 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