tracing: Fix some errors in histogram documentation
Fix typos, inconsistencies in using quotes, incorrect section number, etc. in the trace histogram documentation. Link: http://lkml.kernel.org/r/20180614224859.55864-1-joel@joelfernandes.org Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org> Acked-by: Tom Zanussi <tom.zanussi@linux.intel.com> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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@ -1729,35 +1729,35 @@ If a variable isn't a key variable or prefixed with 'vals=', the
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associated event field will be saved in a variable but won't be summed
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as a value:
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# echo 'hist:keys=next_pid:ts1=common_timestamp ... >> event/trigger
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# echo 'hist:keys=next_pid:ts1=common_timestamp ...' >> event/trigger
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Multiple variables can be assigned at the same time. The below would
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result in both ts0 and b being created as variables, with both
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common_timestamp and field1 additionally being summed as values:
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# echo 'hist:keys=pid:vals=$ts0,$b:ts0=common_timestamp,b=field1 ... >> \
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# echo 'hist:keys=pid:vals=$ts0,$b:ts0=common_timestamp,b=field1 ...' >> \
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event/trigger
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Note that variable assignments can appear either preceding or
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following their use. The command below behaves identically to the
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command above:
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# echo 'hist:keys=pid:ts0=common_timestamp,b=field1:vals=$ts0,$b ... >> \
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# echo 'hist:keys=pid:ts0=common_timestamp,b=field1:vals=$ts0,$b ...' >> \
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event/trigger
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Any number of variables not bound to a 'vals=' prefix can also be
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assigned by simply separating them with colons. Below is the same
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thing but without the values being summed in the histogram:
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# echo 'hist:keys=pid:ts0=common_timestamp:b=field1 ... >> event/trigger
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# echo 'hist:keys=pid:ts0=common_timestamp:b=field1 ...' >> event/trigger
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Variables set as above can be referenced and used in expressions on
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another event.
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For example, here's how a latency can be calculated:
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# echo 'hist:keys=pid,prio:ts0=common_timestamp ... >> event1/trigger
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# echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ... >> event2/trigger
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# echo 'hist:keys=pid,prio:ts0=common_timestamp ...' >> event1/trigger
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# echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ...' >> event2/trigger
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In the first line above, the event's timetamp is saved into the
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variable ts0. In the next line, ts0 is subtracted from the second
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@ -1766,7 +1766,7 @@ yet another variable, 'wakeup_lat'. The hist trigger below in turn
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makes use of the wakeup_lat variable to compute a combined latency
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using the same key and variable from yet another event:
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# echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ... >> event3/trigger
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# echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ...' >> event3/trigger
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2.2.2 Synthetic Events
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----------------------
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@ -1807,10 +1807,11 @@ the command that defined it with a '!':
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At this point, there isn't yet an actual 'wakeup_latency' event
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instantiated in the event subsytem - for this to happen, a 'hist
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trigger action' needs to be instantiated and bound to actual fields
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and variables defined on other events (see Section 6.3.3 below).
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and variables defined on other events (see Section 2.2.3 below on
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how that is done using hist trigger 'onmatch' action). Once that is
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done, the 'wakeup_latency' synthetic event instance is created.
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Once that is done, an event instance is created, and a histogram can
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be defined using it:
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A histogram can now be defined for the new synthetic event:
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# echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \
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/sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
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@ -1960,7 +1961,7 @@ hist trigger specification.
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back to that pid, the timestamp difference is calculated. If the
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resulting latency, stored in wakeup_lat, exceeds the current
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maximum latency, the values specified in the save() fields are
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recoreded:
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recorded:
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# echo 'hist:keys=pid:ts0=common_timestamp.usecs \
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if comm=="cyclictest"' >> \
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