Documentation/trace/boottime-trace.rst

128 Ftrace Histogram Options
131 Since it is too long to write a histogram action as a string for per-event
133 for the histogram actions. For the detail of the each parameter,
134 please read the event histogram document (Documentation/trace/histogram.rst)
137   Set histogram key parameters. (Mandatory)
138   The 'N' is a digit string for the multiple histogram. You can omit it
139   if there is one histogram on the event.
142   Set histogram value parameters.
145   Set histogram sort parameter options.
148   Set histogram size (number of entries).
151   Set histogram name.
157   Set histogram control parameter. You can set one of them.
160   Set histogram 'onmatch' handler matching event parameter.
162   if there is one 'onmatch' handler on this histogram.
165   Set histogram 'trace' action for 'onmatch'.
170   Set histogram 'onmax' handler variable parameter.
173   Set histogram 'onchange' handler variable parameter.
176   Set histogram 'save' action parameters for 'onmax' or 'onchange' handler.
181   Set histogram 'snapshot' action for 'onmax' or 'onchange' handler.
186   Set histogram filter expression. You don't need 'if' in the FILTER_EXPR.
189 option if the 'actions' option has a histogram action.
210 events, and synthetic events with histogram, write a boot config like