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| author | Tom Zanussi <tom.zanussi@linux.intel.com> | 2018-01-16 03:52:08 +0100 |
|---|---|---|
| committer | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2018-03-10 22:06:03 +0100 |
| commit | a4072fe85ba3671720cab0788291af953db27318 (patch) | |
| tree | c96d124bab2370cb3ddb70bb8fe6f130c9a609ab /Documentation | |
| parent | tracing: Make tracing_set_clock() non-static (diff) | |
| download | linux-a4072fe85ba3671720cab0788291af953db27318.tar.xz linux-a4072fe85ba3671720cab0788291af953db27318.zip | |
tracing: Add a clock attribute for hist triggers
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>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/trace/histogram.txt | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt index df08882d091c..6e05510afc28 100644 --- a/Documentation/trace/histogram.txt +++ b/Documentation/trace/histogram.txt @@ -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 ------------------------- |