On Wed, 16 Oct 2024 19:49:15 +0900 "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote: > Overview > -------- > This patch set allows user to `poll`(or `select`, `epoll`) on event > histogram interface. As you know each event has its own `hist` file > which shows histograms generated by trigger action. So user can set > a new hist trigger on any event you want to monitor, and poll on the > `hist` file until it is updated. Note: This `hist` is not disabled by tracing_on interface, because that interface only disables `recording`. Thus to monitor events via this interface, user must ensure the tracing_on is enabled, also, set the same "filter" to the hist action. Thank you, > > There are 2 poll events are supported, POLLIN and POLLPRI. POLLIN > means that there are any readable update on `hist` file and this > event will be flashed only when you call read(). So, this is > useful if you want to read the histogram periodically. > The other POLLPRI event is for monitoring trace event. Like the > POLLIN, this will be returned when the histogram is updated, but > you don't need to read() the file and use poll() again. > > Note that this waits for histogram update (not event arrival), thus > you must set a histogram on the event at first. > > Usage > ----- > Here is an example usage: > > ---- > TRACEFS=/sys/kernel/tracing > EVENT=$TRACEFS/events/sched/sched_process_free > > # setup histogram trigger and enable event > echo "hist:key=comm" >> $EVENT/trigger > echo 1 > $EVENT/enable > > # Wait for update > poll pri $EVENT/hist > > # Event arrived. > echo "process free event is comming" > tail $TRACEFS/trace > ---- > > The 'poll' command is in the selftest patch. > > You can take this series also from here; > > https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git/log/?h=topic/event-hist-poll > > Thank you, > --- > > Masami Hiramatsu (Google) (3): > tracing/hist: Add poll(POLLIN) support on hist file > tracing/hist: Support POLLPRI event for poll on histogram > selftests/tracing: Add hist poll() support test > > > include/linux/trace_events.h | 14 +++ > kernel/trace/trace_events.c | 14 +++ > kernel/trace/trace_events_hist.c | 100 +++++++++++++++++++- > tools/testing/selftests/ftrace/Makefile | 2 > tools/testing/selftests/ftrace/poll.c | 74 +++++++++++++++ > .../ftrace/test.d/trigger/trigger-hist-poll.tc | 74 +++++++++++++++ > 6 files changed, 275 insertions(+), 3 deletions(-) > create mode 100644 tools/testing/selftests/ftrace/poll.c > create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc > > -- > Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
