On Mon, 14 May 2018 16:47:07 -0500
Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx> wrote:
> Hi Steve,
>
> This is a nice new event feature - thanks for doing it! Some minor typo
> comments below..
Can I get an Acked-by from you?
> > +3. User space creating a trigger
> > +--------------------------------
> > +
> > +Writing into /sys/kernel/tracing/trace_marker writes into the ftrace
> > +ring buffer. This can also act like an event, by writing into the trigger
> > +file located in /sys/kernel/tracing/events/ftrace/print/
> > +
> > +Modifying cyclictest to write into the trace_marker file before it sleeps
> > +and after it wakes up, something like this:
> > +
> > +static void traceputs(char *str)
> > +{
> > + /* tracemark_fd is the trace_marker file descripto */
> >
>
> Should be 'descriptor'?
Fixed.
> > + # ./cyclictest -p80 -d0 -i250 -n -a -t --tracemark -b 1000
> > +
> > + -p80 : run threads at priority 80
> > + -d0 : have all threads run at the same interval
> > + -i250 : start the interval at 250 microseconds (all threads will do this)
> > + -n : sleep with nanosleep
> > + -a : affine all threads to a separate CPU
> > + -t : one thread per available CPU
> > + --tracemark : enable trace mark writing
> > + -b 1000 : stop if any latency is greater than 1000 microseconds
> > +
> > +Note, the -b 1000 is used just to make --tracemark available.
> > +
> > +The we can see the histogram created by this with:
> > +
>
> 'Then we can..
Fixed
> > +The difference this time is that instead of using the trace_marker to start
> > +the latency, the sched_waking event is used, matching the common_pid for the
> > +trace_marker write with the pid that is being worken by sched_waking.
> >
>
> s/worken/woken ?
Fixed. (It's kind of like Borken)
>
> >
> > +
> > +After running cyclictest again with the same parameters, we now have:
> > +
> > + # cat events/synthetic/latency/hist
> > +# event histogram
> > +#
> > +# trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active]
> > +#
> > +
> > +{ lat: 7, common_pid: 2302 } hitcount: 640
> >
>
> snip
>
> >
> > +{ lat: 61, common_pid: 2302 } hitcount: 1
> > +{ lat: 110, common_pid: 2302 } hitcount: 1
> > +
> > +Totals:
> > + Hits: 89565
> > + Entries: 158
> > + Dropped: 0
> > +
> > +This doesn't tell us any information about how late cyclictest may have
> > +worken up, but it does show us a nice histogram of how long it took from
> > +the time that cyclictest was worken to the time it made it into user space.
> >
>
> A couple more that don't seem to be 'worken' ;-)
I have an itchy 'r' finger.
Thanks for the review, I just updated this.
Oh, I guess I think I prefer a "Reviewed-by" tag instead of Ack (gives
a stronger meaning).
-- Steve
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