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Message-ID: <20180516114207.60c7e8a8@gandalf.local.home>
Date: Wed, 16 May 2018 11:42:07 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org
Cc: Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Tom Zanussi <tom.zanussi@...ux.intel.com>,
Clark Williams <williams@...hat.com>,
Karim Yaghmour <karim.yaghmour@...rsys.com>,
Brendan Gregg <bgregg@...flix.com>,
Joel Fernandes <joel@...lfernandes.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Yann Ylavic <ylavic.dev@...il.com>,
linux-rt-users@...r.kernel.org
Subject: [PATCH v3.5 10/14] tracing: Document trace_marker triggers
From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Add documentation and an example on how to use trace_marker triggers.
Reviewed-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
Sending this as 3.5 as I don't want to spam for a simple change.
Changes from v3:
- Removed cut and paste extra line to remove a histogram trigger (Tom Zanussi)
Documentation/trace/events.rst | 6 +-
Documentation/trace/ftrace.rst | 5 +
Documentation/trace/histogram.txt | 545 +++++++++++++++++++++++++++++++++++++-
3 files changed, 554 insertions(+), 2 deletions(-)
diff --git a/Documentation/trace/events.rst b/Documentation/trace/events.rst
index a5ea2cb0082b..1afae55dc55c 100644
--- a/Documentation/trace/events.rst
+++ b/Documentation/trace/events.rst
@@ -338,10 +338,14 @@ used for conditionally invoking triggers.
The syntax for event triggers is roughly based on the syntax for
set_ftrace_filter 'ftrace filter commands' (see the 'Filter commands'
-section of Documentation/trace/ftrace.txt), but there are major
+section of Documentation/trace/ftrace.rst), but there are major
differences and the implementation isn't currently tied to it in any
way, so beware about making generalizations between the two.
+Note: Writing into trace_marker (See Documentation/trace/ftrace.rst)
+ can also enable triggers that are written into
+ /sys/kernel/tracing/events/ftrace/print/trigger
+
6.1 Expression syntax
---------------------
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index 67d9c38e95eb..aad4776c0f5d 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -507,6 +507,11 @@ of ftrace. Here is a list of some of the key files:
trace_fd = open("trace_marker", WR_ONLY);
+ Note: Writing into the trace_marker file can also initiate triggers
+ that are written into /sys/kernel/tracing/events/ftrace/print/trigger
+ See "Event triggers" in Documentation/trace/events.rst and an
+ example in Documentation/trace/histogram.rst (Section 3.)
+
trace_marker_raw:
This is similar to trace_marker above, but is meant for for binary data
diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt
index 6e05510afc28..b13771cb12c1 100644
--- a/Documentation/trace/histogram.txt
+++ b/Documentation/trace/histogram.txt
@@ -1604,7 +1604,6 @@
Entries: 7
Dropped: 0
-
2.2 Inter-event hist triggers
-----------------------------
@@ -1993,3 +1992,547 @@ hist trigger specification.
Hits: 12970
Entries: 2
Dropped: 0
+
+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 descriptor */
+ if (tracemark_fd < 0)
+ return;
+ /* write the tracemark message */
+ write(tracemark_fd, str, strlen(str));
+}
+
+And later add something like:
+
+ traceputs("start");
+ clock_nanosleep(...);
+ traceputs("end");
+
+We can make a histogram from this:
+
+ # cd /sys/kernel/tracing
+ # echo 'latency u64 lat' > synthetic_events
+ # echo 'hist:keys=common_pid:ts0=common_timestamp.usecs if buf == "start"' > events/ftrace/print/trigger
+ # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(ftrace.print).latency($lat) if buf == "end"' >> events/ftrace/print/trigger
+ # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger
+
+The above created a synthetic event called "latency" and two histograms
+against the trace_marker, one gets triggered when "start" is written into the
+trace_marker file and the other when "end" is written. If the pids match, then
+it will call the "latency" synthetic event with the calculated latency as its
+parameter. Finally, a histogram is added to the latency synthetic event to
+record the calculated latency along with the pid.
+
+Now running cyclictest with:
+
+ # ./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.
+
+Then we can see the histogram created by this with:
+
+ # cat events/synthetic/latency/hist
+# event histogram
+#
+# trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active]
+#
+
+{ lat: 107, common_pid: 2039 } hitcount: 1
+{ lat: 122, common_pid: 2041 } hitcount: 1
+{ lat: 166, common_pid: 2039 } hitcount: 1
+{ lat: 174, common_pid: 2039 } hitcount: 1
+{ lat: 194, common_pid: 2041 } hitcount: 1
+{ lat: 196, common_pid: 2036 } hitcount: 1
+{ lat: 197, common_pid: 2038 } hitcount: 1
+{ lat: 198, common_pid: 2039 } hitcount: 1
+{ lat: 199, common_pid: 2039 } hitcount: 1
+{ lat: 200, common_pid: 2041 } hitcount: 1
+{ lat: 201, common_pid: 2039 } hitcount: 2
+{ lat: 202, common_pid: 2038 } hitcount: 1
+{ lat: 202, common_pid: 2043 } hitcount: 1
+{ lat: 203, common_pid: 2039 } hitcount: 1
+{ lat: 203, common_pid: 2036 } hitcount: 1
+{ lat: 203, common_pid: 2041 } hitcount: 1
+{ lat: 206, common_pid: 2038 } hitcount: 2
+{ lat: 207, common_pid: 2039 } hitcount: 1
+{ lat: 207, common_pid: 2036 } hitcount: 1
+{ lat: 208, common_pid: 2040 } hitcount: 1
+{ lat: 209, common_pid: 2043 } hitcount: 1
+{ lat: 210, common_pid: 2039 } hitcount: 1
+{ lat: 211, common_pid: 2039 } hitcount: 4
+{ lat: 212, common_pid: 2043 } hitcount: 1
+{ lat: 212, common_pid: 2039 } hitcount: 2
+{ lat: 213, common_pid: 2039 } hitcount: 1
+{ lat: 214, common_pid: 2038 } hitcount: 1
+{ lat: 214, common_pid: 2039 } hitcount: 2
+{ lat: 214, common_pid: 2042 } hitcount: 1
+{ lat: 215, common_pid: 2039 } hitcount: 1
+{ lat: 217, common_pid: 2036 } hitcount: 1
+{ lat: 217, common_pid: 2040 } hitcount: 1
+{ lat: 217, common_pid: 2039 } hitcount: 1
+{ lat: 218, common_pid: 2039 } hitcount: 6
+{ lat: 219, common_pid: 2039 } hitcount: 9
+{ lat: 220, common_pid: 2039 } hitcount: 11
+{ lat: 221, common_pid: 2039 } hitcount: 5
+{ lat: 221, common_pid: 2042 } hitcount: 1
+{ lat: 222, common_pid: 2039 } hitcount: 7
+{ lat: 223, common_pid: 2036 } hitcount: 1
+{ lat: 223, common_pid: 2039 } hitcount: 3
+{ lat: 224, common_pid: 2039 } hitcount: 4
+{ lat: 224, common_pid: 2037 } hitcount: 1
+{ lat: 224, common_pid: 2036 } hitcount: 2
+{ lat: 225, common_pid: 2039 } hitcount: 5
+{ lat: 225, common_pid: 2042 } hitcount: 1
+{ lat: 226, common_pid: 2039 } hitcount: 7
+{ lat: 226, common_pid: 2036 } hitcount: 4
+{ lat: 227, common_pid: 2039 } hitcount: 6
+{ lat: 227, common_pid: 2036 } hitcount: 12
+{ lat: 227, common_pid: 2043 } hitcount: 1
+{ lat: 228, common_pid: 2039 } hitcount: 7
+{ lat: 228, common_pid: 2036 } hitcount: 14
+{ lat: 229, common_pid: 2039 } hitcount: 9
+{ lat: 229, common_pid: 2036 } hitcount: 8
+{ lat: 229, common_pid: 2038 } hitcount: 1
+{ lat: 230, common_pid: 2039 } hitcount: 11
+{ lat: 230, common_pid: 2036 } hitcount: 6
+{ lat: 230, common_pid: 2043 } hitcount: 1
+{ lat: 230, common_pid: 2042 } hitcount: 2
+{ lat: 231, common_pid: 2041 } hitcount: 1
+{ lat: 231, common_pid: 2036 } hitcount: 6
+{ lat: 231, common_pid: 2043 } hitcount: 1
+{ lat: 231, common_pid: 2039 } hitcount: 8
+{ lat: 232, common_pid: 2037 } hitcount: 1
+{ lat: 232, common_pid: 2039 } hitcount: 6
+{ lat: 232, common_pid: 2040 } hitcount: 2
+{ lat: 232, common_pid: 2036 } hitcount: 5
+{ lat: 232, common_pid: 2043 } hitcount: 1
+{ lat: 233, common_pid: 2036 } hitcount: 5
+{ lat: 233, common_pid: 2039 } hitcount: 11
+{ lat: 234, common_pid: 2039 } hitcount: 4
+{ lat: 234, common_pid: 2038 } hitcount: 2
+{ lat: 234, common_pid: 2043 } hitcount: 2
+{ lat: 234, common_pid: 2036 } hitcount: 11
+{ lat: 234, common_pid: 2040 } hitcount: 1
+{ lat: 235, common_pid: 2037 } hitcount: 2
+{ lat: 235, common_pid: 2036 } hitcount: 8
+{ lat: 235, common_pid: 2043 } hitcount: 2
+{ lat: 235, common_pid: 2039 } hitcount: 5
+{ lat: 235, common_pid: 2042 } hitcount: 2
+{ lat: 235, common_pid: 2040 } hitcount: 4
+{ lat: 235, common_pid: 2041 } hitcount: 1
+{ lat: 236, common_pid: 2036 } hitcount: 7
+{ lat: 236, common_pid: 2037 } hitcount: 1
+{ lat: 236, common_pid: 2041 } hitcount: 5
+{ lat: 236, common_pid: 2039 } hitcount: 3
+{ lat: 236, common_pid: 2043 } hitcount: 9
+{ lat: 236, common_pid: 2040 } hitcount: 7
+{ lat: 237, common_pid: 2037 } hitcount: 1
+{ lat: 237, common_pid: 2040 } hitcount: 1
+{ lat: 237, common_pid: 2036 } hitcount: 9
+{ lat: 237, common_pid: 2039 } hitcount: 3
+{ lat: 237, common_pid: 2043 } hitcount: 8
+{ lat: 237, common_pid: 2042 } hitcount: 2
+{ lat: 237, common_pid: 2041 } hitcount: 2
+{ lat: 238, common_pid: 2043 } hitcount: 10
+{ lat: 238, common_pid: 2040 } hitcount: 1
+{ lat: 238, common_pid: 2037 } hitcount: 9
+{ lat: 238, common_pid: 2038 } hitcount: 1
+{ lat: 238, common_pid: 2039 } hitcount: 1
+{ lat: 238, common_pid: 2042 } hitcount: 3
+{ lat: 238, common_pid: 2036 } hitcount: 7
+{ lat: 239, common_pid: 2041 } hitcount: 1
+{ lat: 239, common_pid: 2043 } hitcount: 11
+{ lat: 239, common_pid: 2037 } hitcount: 11
+{ lat: 239, common_pid: 2038 } hitcount: 6
+{ lat: 239, common_pid: 2036 } hitcount: 7
+{ lat: 239, common_pid: 2040 } hitcount: 1
+{ lat: 239, common_pid: 2042 } hitcount: 9
+{ lat: 240, common_pid: 2037 } hitcount: 29
+{ lat: 240, common_pid: 2043 } hitcount: 15
+{ lat: 240, common_pid: 2040 } hitcount: 44
+{ lat: 240, common_pid: 2039 } hitcount: 1
+{ lat: 240, common_pid: 2041 } hitcount: 2
+{ lat: 240, common_pid: 2038 } hitcount: 1
+{ lat: 240, common_pid: 2036 } hitcount: 10
+{ lat: 240, common_pid: 2042 } hitcount: 13
+{ lat: 241, common_pid: 2036 } hitcount: 21
+{ lat: 241, common_pid: 2041 } hitcount: 36
+{ lat: 241, common_pid: 2037 } hitcount: 34
+{ lat: 241, common_pid: 2042 } hitcount: 14
+{ lat: 241, common_pid: 2040 } hitcount: 94
+{ lat: 241, common_pid: 2039 } hitcount: 12
+{ lat: 241, common_pid: 2038 } hitcount: 2
+{ lat: 241, common_pid: 2043 } hitcount: 28
+{ lat: 242, common_pid: 2040 } hitcount: 109
+{ lat: 242, common_pid: 2041 } hitcount: 506
+{ lat: 242, common_pid: 2039 } hitcount: 155
+{ lat: 242, common_pid: 2042 } hitcount: 21
+{ lat: 242, common_pid: 2037 } hitcount: 52
+{ lat: 242, common_pid: 2043 } hitcount: 21
+{ lat: 242, common_pid: 2036 } hitcount: 16
+{ lat: 242, common_pid: 2038 } hitcount: 156
+{ lat: 243, common_pid: 2037 } hitcount: 46
+{ lat: 243, common_pid: 2039 } hitcount: 40
+{ lat: 243, common_pid: 2042 } hitcount: 119
+{ lat: 243, common_pid: 2041 } hitcount: 611
+{ lat: 243, common_pid: 2036 } hitcount: 69
+{ lat: 243, common_pid: 2038 } hitcount: 784
+{ lat: 243, common_pid: 2040 } hitcount: 323
+{ lat: 243, common_pid: 2043 } hitcount: 14
+{ lat: 244, common_pid: 2043 } hitcount: 35
+{ lat: 244, common_pid: 2042 } hitcount: 305
+{ lat: 244, common_pid: 2039 } hitcount: 8
+{ lat: 244, common_pid: 2040 } hitcount: 4515
+{ lat: 244, common_pid: 2038 } hitcount: 371
+{ lat: 244, common_pid: 2037 } hitcount: 31
+{ lat: 244, common_pid: 2036 } hitcount: 114
+{ lat: 244, common_pid: 2041 } hitcount: 3396
+{ lat: 245, common_pid: 2036 } hitcount: 700
+{ lat: 245, common_pid: 2041 } hitcount: 2772
+{ lat: 245, common_pid: 2037 } hitcount: 268
+{ lat: 245, common_pid: 2039 } hitcount: 472
+{ lat: 245, common_pid: 2038 } hitcount: 2758
+{ lat: 245, common_pid: 2042 } hitcount: 3833
+{ lat: 245, common_pid: 2040 } hitcount: 3105
+{ lat: 245, common_pid: 2043 } hitcount: 645
+{ lat: 246, common_pid: 2038 } hitcount: 3451
+{ lat: 246, common_pid: 2041 } hitcount: 142
+{ lat: 246, common_pid: 2037 } hitcount: 5101
+{ lat: 246, common_pid: 2040 } hitcount: 68
+{ lat: 246, common_pid: 2043 } hitcount: 5099
+{ lat: 246, common_pid: 2039 } hitcount: 5608
+{ lat: 246, common_pid: 2042 } hitcount: 3723
+{ lat: 246, common_pid: 2036 } hitcount: 4738
+{ lat: 247, common_pid: 2042 } hitcount: 312
+{ lat: 247, common_pid: 2043 } hitcount: 2385
+{ lat: 247, common_pid: 2041 } hitcount: 452
+{ lat: 247, common_pid: 2038 } hitcount: 792
+{ lat: 247, common_pid: 2040 } hitcount: 78
+{ lat: 247, common_pid: 2036 } hitcount: 2375
+{ lat: 247, common_pid: 2039 } hitcount: 1834
+{ lat: 247, common_pid: 2037 } hitcount: 2655
+{ lat: 248, common_pid: 2037 } hitcount: 36
+{ lat: 248, common_pid: 2042 } hitcount: 11
+{ lat: 248, common_pid: 2038 } hitcount: 122
+{ lat: 248, common_pid: 2036 } hitcount: 135
+{ lat: 248, common_pid: 2039 } hitcount: 26
+{ lat: 248, common_pid: 2041 } hitcount: 503
+{ lat: 248, common_pid: 2043 } hitcount: 66
+{ lat: 248, common_pid: 2040 } hitcount: 46
+{ lat: 249, common_pid: 2037 } hitcount: 29
+{ lat: 249, common_pid: 2038 } hitcount: 1
+{ lat: 249, common_pid: 2043 } hitcount: 29
+{ lat: 249, common_pid: 2039 } hitcount: 8
+{ lat: 249, common_pid: 2042 } hitcount: 56
+{ lat: 249, common_pid: 2040 } hitcount: 27
+{ lat: 249, common_pid: 2041 } hitcount: 11
+{ lat: 249, common_pid: 2036 } hitcount: 27
+{ lat: 250, common_pid: 2038 } hitcount: 1
+{ lat: 250, common_pid: 2036 } hitcount: 30
+{ lat: 250, common_pid: 2040 } hitcount: 19
+{ lat: 250, common_pid: 2043 } hitcount: 22
+{ lat: 250, common_pid: 2042 } hitcount: 20
+{ lat: 250, common_pid: 2041 } hitcount: 1
+{ lat: 250, common_pid: 2039 } hitcount: 6
+{ lat: 250, common_pid: 2037 } hitcount: 48
+{ lat: 251, common_pid: 2037 } hitcount: 43
+{ lat: 251, common_pid: 2039 } hitcount: 1
+{ lat: 251, common_pid: 2036 } hitcount: 12
+{ lat: 251, common_pid: 2042 } hitcount: 2
+{ lat: 251, common_pid: 2041 } hitcount: 1
+{ lat: 251, common_pid: 2043 } hitcount: 15
+{ lat: 251, common_pid: 2040 } hitcount: 3
+{ lat: 252, common_pid: 2040 } hitcount: 1
+{ lat: 252, common_pid: 2036 } hitcount: 12
+{ lat: 252, common_pid: 2037 } hitcount: 21
+{ lat: 252, common_pid: 2043 } hitcount: 14
+{ lat: 253, common_pid: 2037 } hitcount: 21
+{ lat: 253, common_pid: 2039 } hitcount: 2
+{ lat: 253, common_pid: 2036 } hitcount: 9
+{ lat: 253, common_pid: 2043 } hitcount: 6
+{ lat: 253, common_pid: 2040 } hitcount: 1
+{ lat: 254, common_pid: 2036 } hitcount: 8
+{ lat: 254, common_pid: 2043 } hitcount: 3
+{ lat: 254, common_pid: 2041 } hitcount: 1
+{ lat: 254, common_pid: 2042 } hitcount: 1
+{ lat: 254, common_pid: 2039 } hitcount: 1
+{ lat: 254, common_pid: 2037 } hitcount: 12
+{ lat: 255, common_pid: 2043 } hitcount: 1
+{ lat: 255, common_pid: 2037 } hitcount: 2
+{ lat: 255, common_pid: 2036 } hitcount: 2
+{ lat: 255, common_pid: 2039 } hitcount: 8
+{ lat: 256, common_pid: 2043 } hitcount: 1
+{ lat: 256, common_pid: 2036 } hitcount: 4
+{ lat: 256, common_pid: 2039 } hitcount: 6
+{ lat: 257, common_pid: 2039 } hitcount: 5
+{ lat: 257, common_pid: 2036 } hitcount: 4
+{ lat: 258, common_pid: 2039 } hitcount: 5
+{ lat: 258, common_pid: 2036 } hitcount: 2
+{ lat: 259, common_pid: 2036 } hitcount: 7
+{ lat: 259, common_pid: 2039 } hitcount: 7
+{ lat: 260, common_pid: 2036 } hitcount: 8
+{ lat: 260, common_pid: 2039 } hitcount: 6
+{ lat: 261, common_pid: 2036 } hitcount: 5
+{ lat: 261, common_pid: 2039 } hitcount: 7
+{ lat: 262, common_pid: 2039 } hitcount: 5
+{ lat: 262, common_pid: 2036 } hitcount: 5
+{ lat: 263, common_pid: 2039 } hitcount: 7
+{ lat: 263, common_pid: 2036 } hitcount: 7
+{ lat: 264, common_pid: 2039 } hitcount: 9
+{ lat: 264, common_pid: 2036 } hitcount: 9
+{ lat: 265, common_pid: 2036 } hitcount: 5
+{ lat: 265, common_pid: 2039 } hitcount: 1
+{ lat: 266, common_pid: 2036 } hitcount: 1
+{ lat: 266, common_pid: 2039 } hitcount: 3
+{ lat: 267, common_pid: 2036 } hitcount: 1
+{ lat: 267, common_pid: 2039 } hitcount: 3
+{ lat: 268, common_pid: 2036 } hitcount: 1
+{ lat: 268, common_pid: 2039 } hitcount: 6
+{ lat: 269, common_pid: 2036 } hitcount: 1
+{ lat: 269, common_pid: 2043 } hitcount: 1
+{ lat: 269, common_pid: 2039 } hitcount: 2
+{ lat: 270, common_pid: 2040 } hitcount: 1
+{ lat: 270, common_pid: 2039 } hitcount: 6
+{ lat: 271, common_pid: 2041 } hitcount: 1
+{ lat: 271, common_pid: 2039 } hitcount: 5
+{ lat: 272, common_pid: 2039 } hitcount: 10
+{ lat: 273, common_pid: 2039 } hitcount: 8
+{ lat: 274, common_pid: 2039 } hitcount: 2
+{ lat: 275, common_pid: 2039 } hitcount: 1
+{ lat: 276, common_pid: 2039 } hitcount: 2
+{ lat: 276, common_pid: 2037 } hitcount: 1
+{ lat: 276, common_pid: 2038 } hitcount: 1
+{ lat: 277, common_pid: 2039 } hitcount: 1
+{ lat: 277, common_pid: 2042 } hitcount: 1
+{ lat: 278, common_pid: 2039 } hitcount: 1
+{ lat: 279, common_pid: 2039 } hitcount: 4
+{ lat: 279, common_pid: 2043 } hitcount: 1
+{ lat: 280, common_pid: 2039 } hitcount: 3
+{ lat: 283, common_pid: 2036 } hitcount: 2
+{ lat: 284, common_pid: 2039 } hitcount: 1
+{ lat: 284, common_pid: 2043 } hitcount: 1
+{ lat: 288, common_pid: 2039 } hitcount: 1
+{ lat: 289, common_pid: 2039 } hitcount: 1
+{ lat: 300, common_pid: 2039 } hitcount: 1
+{ lat: 384, common_pid: 2039 } hitcount: 1
+
+Totals:
+ Hits: 67625
+ Entries: 278
+ Dropped: 0
+
+Note, the writes are around the sleep, so ideally they will all be of 250
+microseconds. If you are wondering how there are several that are under
+250 microseconds, that is because the way cyclictest works, is if one
+iteration comes in late, the next one will set the timer to wake up less that
+250. That is, if an iteration came in 50 microseconds late, the next wake up
+will be at 200 microseconds.
+
+But this could easily be done in userspace. To make this even more
+interesting, we can mix the histogram between events that happened in the
+kernel with trace_marker.
+
+ # cd /sys/kernel/tracing
+ # echo 'latency u64 lat' > synthetic_events
+ # echo 'hist:keys=pid:ts0=common_timestamp.usecs' > events/sched/sched_waking/trigger
+ # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(sched.sched_waking).latency($lat) if buf == "end"' > events/ftrace/print/trigger
+ # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger
+
+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 woken by sched_waking.
+
+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
+{ lat: 7, common_pid: 2299 } hitcount: 42
+{ lat: 7, common_pid: 2303 } hitcount: 18
+{ lat: 7, common_pid: 2305 } hitcount: 166
+{ lat: 7, common_pid: 2306 } hitcount: 1
+{ lat: 7, common_pid: 2301 } hitcount: 91
+{ lat: 7, common_pid: 2300 } hitcount: 17
+{ lat: 8, common_pid: 2303 } hitcount: 8296
+{ lat: 8, common_pid: 2304 } hitcount: 6864
+{ lat: 8, common_pid: 2305 } hitcount: 9464
+{ lat: 8, common_pid: 2301 } hitcount: 9213
+{ lat: 8, common_pid: 2306 } hitcount: 6246
+{ lat: 8, common_pid: 2302 } hitcount: 8797
+{ lat: 8, common_pid: 2299 } hitcount: 8771
+{ lat: 8, common_pid: 2300 } hitcount: 8119
+{ lat: 9, common_pid: 2305 } hitcount: 1519
+{ lat: 9, common_pid: 2299 } hitcount: 2346
+{ lat: 9, common_pid: 2303 } hitcount: 2841
+{ lat: 9, common_pid: 2301 } hitcount: 1846
+{ lat: 9, common_pid: 2304 } hitcount: 3861
+{ lat: 9, common_pid: 2302 } hitcount: 1210
+{ lat: 9, common_pid: 2300 } hitcount: 2762
+{ lat: 9, common_pid: 2306 } hitcount: 4247
+{ lat: 10, common_pid: 2299 } hitcount: 16
+{ lat: 10, common_pid: 2306 } hitcount: 333
+{ lat: 10, common_pid: 2303 } hitcount: 16
+{ lat: 10, common_pid: 2304 } hitcount: 168
+{ lat: 10, common_pid: 2302 } hitcount: 240
+{ lat: 10, common_pid: 2301 } hitcount: 28
+{ lat: 10, common_pid: 2300 } hitcount: 95
+{ lat: 10, common_pid: 2305 } hitcount: 18
+{ lat: 11, common_pid: 2303 } hitcount: 5
+{ lat: 11, common_pid: 2305 } hitcount: 8
+{ lat: 11, common_pid: 2306 } hitcount: 221
+{ lat: 11, common_pid: 2302 } hitcount: 76
+{ lat: 11, common_pid: 2304 } hitcount: 26
+{ lat: 11, common_pid: 2300 } hitcount: 125
+{ lat: 11, common_pid: 2299 } hitcount: 2
+{ lat: 12, common_pid: 2305 } hitcount: 3
+{ lat: 12, common_pid: 2300 } hitcount: 6
+{ lat: 12, common_pid: 2306 } hitcount: 90
+{ lat: 12, common_pid: 2302 } hitcount: 4
+{ lat: 12, common_pid: 2303 } hitcount: 1
+{ lat: 12, common_pid: 2304 } hitcount: 122
+{ lat: 13, common_pid: 2300 } hitcount: 12
+{ lat: 13, common_pid: 2301 } hitcount: 1
+{ lat: 13, common_pid: 2306 } hitcount: 32
+{ lat: 13, common_pid: 2302 } hitcount: 5
+{ lat: 13, common_pid: 2305 } hitcount: 1
+{ lat: 13, common_pid: 2303 } hitcount: 1
+{ lat: 13, common_pid: 2304 } hitcount: 61
+{ lat: 14, common_pid: 2303 } hitcount: 4
+{ lat: 14, common_pid: 2306 } hitcount: 5
+{ lat: 14, common_pid: 2305 } hitcount: 4
+{ lat: 14, common_pid: 2304 } hitcount: 62
+{ lat: 14, common_pid: 2302 } hitcount: 19
+{ lat: 14, common_pid: 2300 } hitcount: 33
+{ lat: 14, common_pid: 2299 } hitcount: 1
+{ lat: 14, common_pid: 2301 } hitcount: 4
+{ lat: 15, common_pid: 2305 } hitcount: 1
+{ lat: 15, common_pid: 2302 } hitcount: 25
+{ lat: 15, common_pid: 2300 } hitcount: 11
+{ lat: 15, common_pid: 2299 } hitcount: 5
+{ lat: 15, common_pid: 2301 } hitcount: 1
+{ lat: 15, common_pid: 2304 } hitcount: 8
+{ lat: 15, common_pid: 2303 } hitcount: 1
+{ lat: 15, common_pid: 2306 } hitcount: 6
+{ lat: 16, common_pid: 2302 } hitcount: 31
+{ lat: 16, common_pid: 2306 } hitcount: 3
+{ lat: 16, common_pid: 2300 } hitcount: 5
+{ lat: 17, common_pid: 2302 } hitcount: 6
+{ lat: 17, common_pid: 2303 } hitcount: 1
+{ lat: 18, common_pid: 2304 } hitcount: 1
+{ lat: 18, common_pid: 2302 } hitcount: 8
+{ lat: 18, common_pid: 2299 } hitcount: 1
+{ lat: 18, common_pid: 2301 } hitcount: 1
+{ lat: 19, common_pid: 2303 } hitcount: 4
+{ lat: 19, common_pid: 2304 } hitcount: 5
+{ lat: 19, common_pid: 2302 } hitcount: 4
+{ lat: 19, common_pid: 2299 } hitcount: 3
+{ lat: 19, common_pid: 2306 } hitcount: 1
+{ lat: 19, common_pid: 2300 } hitcount: 4
+{ lat: 19, common_pid: 2305 } hitcount: 5
+{ lat: 20, common_pid: 2299 } hitcount: 2
+{ lat: 20, common_pid: 2302 } hitcount: 3
+{ lat: 20, common_pid: 2305 } hitcount: 1
+{ lat: 20, common_pid: 2300 } hitcount: 2
+{ lat: 20, common_pid: 2301 } hitcount: 2
+{ lat: 20, common_pid: 2303 } hitcount: 3
+{ lat: 21, common_pid: 2305 } hitcount: 1
+{ lat: 21, common_pid: 2299 } hitcount: 5
+{ lat: 21, common_pid: 2303 } hitcount: 4
+{ lat: 21, common_pid: 2302 } hitcount: 7
+{ lat: 21, common_pid: 2300 } hitcount: 1
+{ lat: 21, common_pid: 2301 } hitcount: 5
+{ lat: 21, common_pid: 2304 } hitcount: 2
+{ lat: 22, common_pid: 2302 } hitcount: 5
+{ lat: 22, common_pid: 2303 } hitcount: 1
+{ lat: 22, common_pid: 2306 } hitcount: 3
+{ lat: 22, common_pid: 2301 } hitcount: 2
+{ lat: 22, common_pid: 2300 } hitcount: 1
+{ lat: 22, common_pid: 2299 } hitcount: 1
+{ lat: 22, common_pid: 2305 } hitcount: 1
+{ lat: 22, common_pid: 2304 } hitcount: 1
+{ lat: 23, common_pid: 2299 } hitcount: 1
+{ lat: 23, common_pid: 2306 } hitcount: 2
+{ lat: 23, common_pid: 2302 } hitcount: 6
+{ lat: 24, common_pid: 2302 } hitcount: 3
+{ lat: 24, common_pid: 2300 } hitcount: 1
+{ lat: 24, common_pid: 2306 } hitcount: 2
+{ lat: 24, common_pid: 2305 } hitcount: 1
+{ lat: 24, common_pid: 2299 } hitcount: 1
+{ lat: 25, common_pid: 2300 } hitcount: 1
+{ lat: 25, common_pid: 2302 } hitcount: 4
+{ lat: 26, common_pid: 2302 } hitcount: 2
+{ lat: 27, common_pid: 2305 } hitcount: 1
+{ lat: 27, common_pid: 2300 } hitcount: 1
+{ lat: 27, common_pid: 2302 } hitcount: 3
+{ lat: 28, common_pid: 2306 } hitcount: 1
+{ lat: 28, common_pid: 2302 } hitcount: 4
+{ lat: 29, common_pid: 2302 } hitcount: 1
+{ lat: 29, common_pid: 2300 } hitcount: 2
+{ lat: 29, common_pid: 2306 } hitcount: 1
+{ lat: 29, common_pid: 2304 } hitcount: 1
+{ lat: 30, common_pid: 2302 } hitcount: 4
+{ lat: 31, common_pid: 2302 } hitcount: 6
+{ lat: 32, common_pid: 2302 } hitcount: 1
+{ lat: 33, common_pid: 2299 } hitcount: 1
+{ lat: 33, common_pid: 2302 } hitcount: 3
+{ lat: 34, common_pid: 2302 } hitcount: 2
+{ lat: 35, common_pid: 2302 } hitcount: 1
+{ lat: 35, common_pid: 2304 } hitcount: 1
+{ lat: 36, common_pid: 2302 } hitcount: 4
+{ lat: 37, common_pid: 2302 } hitcount: 6
+{ lat: 38, common_pid: 2302 } hitcount: 2
+{ lat: 39, common_pid: 2302 } hitcount: 2
+{ lat: 39, common_pid: 2304 } hitcount: 1
+{ lat: 40, common_pid: 2304 } hitcount: 2
+{ lat: 40, common_pid: 2302 } hitcount: 5
+{ lat: 41, common_pid: 2304 } hitcount: 1
+{ lat: 41, common_pid: 2302 } hitcount: 8
+{ lat: 42, common_pid: 2302 } hitcount: 6
+{ lat: 42, common_pid: 2304 } hitcount: 1
+{ lat: 43, common_pid: 2302 } hitcount: 3
+{ lat: 43, common_pid: 2304 } hitcount: 4
+{ lat: 44, common_pid: 2302 } hitcount: 6
+{ lat: 45, common_pid: 2302 } hitcount: 5
+{ lat: 46, common_pid: 2302 } hitcount: 5
+{ lat: 47, common_pid: 2302 } hitcount: 7
+{ lat: 48, common_pid: 2301 } hitcount: 1
+{ lat: 48, common_pid: 2302 } hitcount: 9
+{ lat: 49, common_pid: 2302 } hitcount: 3
+{ lat: 50, common_pid: 2302 } hitcount: 1
+{ lat: 50, common_pid: 2301 } hitcount: 1
+{ lat: 51, common_pid: 2302 } hitcount: 2
+{ lat: 51, common_pid: 2301 } hitcount: 1
+{ 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
+woken up, but it does show us a nice histogram of how long it took from
+the time that cyclictest was woken to the time it made it into user space.
--
2.13.6
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