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tracing: Add a clock attribute for hist triggers

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The default clock if timestamps are used in a histogram is "global".
If timestamps aren't used, the clock is irrelevant.

Use the "clock=" param only if you want to override the default
"global" clock for a histogram with timestamps.

Link: http://lkml.kernel.org/r/427bed1389c5d22aa40c3e0683e30cc3d151e260.1516069914.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Rajvi Jingar <rajvi.jingar@intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Tom Zanussi
2018-01-15 20:52:08 -06:00
committed by Steven Rostedt (VMware)
parent d71bd34d78
commit a4072fe85b
2 changed files with 49 additions and 4 deletions
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11
Documentation/trace/histogram.txt
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@@ -1671,7 +1671,16 @@ features have been added to the hist trigger support:
it is in units of nanoseconds; appending '.usecs' to a
common_timestamp field changes the units to microseconds.
These features are decribed in more detail in the following sections.
A note on inter-event timestamps: If common_timestamp is used in a
histogram, the trace buffer is automatically switched over to using
absolute timestamps and the "global" trace clock, in order to avoid
bogus timestamp differences with other clocks that aren't coherent
across CPUs. This can be overridden by specifying one of the other
trace clocks instead, using the "clock=XXX" hist trigger attribute,
where XXX is any of the clocks listed in the tracing/trace_clock
pseudo-file.
These features are described in more detail in the following sections.
2.2.1 Histogram Variables
-------------------------