On Mon, 14 May 2018 16:47:07 -0500
Tom Zanussi [off-list ref] 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?

quoted

+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.

quoted

+ # ./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

quoted

+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)

quoted

+
+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

quoted

+{ 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