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tracing: Add hist_debug trace event files for histogram debugging

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Add a new "hist_debug" file for each trace event, which when read will
dump out a bunch of internal details about the hist triggers defined
on that event.

This is normally off but can be enabled by saying 'y' to the new
CONFIG_HIST_TRIGGERS_DEBUG config option.

This is in support of the new Documentation file describing histogram
internals, Documentation/trace/histogram-design.rst, which was
requested by developers trying to understand the internals when
extending or making use of the hist triggers for higher-level tools.

The histogram-design.rst documentation refers to the hist_debug files
and demonstrates their use with output in the test examples.

Link: http://lkml.kernel.org/r/77914c22b0ba493d9783c53bbfbc6087d6a7e1b1.1585941485.git.zanussi@kernel.org

Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Tom Zanussi
2020-04-03 14:31:21 -05:00
committed by Steven Rostedt (VMware)
parent 16b585fe71
commit 2d19bd79ae
4 changed files with 301 additions and 0 deletions
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1
kernel/trace/trace.h
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@@ -1661,6 +1661,7 @@ extern struct list_head ftrace_events;
extern const struct file_operations event_trigger_fops;
extern const struct file_operations event_hist_fops;
extern const struct file_operations event_hist_debug_fops;
extern const struct file_operations event_inject_fops;
#ifdef CONFIG_HIST_TRIGGERS