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Subject[PATCH 19/19] tracing/workqueue: provide documentation for the workqueue tracer
Date
Provide a quick documentation for both stat and event tracing with
the workqueue tracer.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Zhao Lei <zhaolei@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
Documentation/trace/workqueue.txt | 114 +++++++++++++++++++++++++++++++++++++
1 files changed, 114 insertions(+), 0 deletions(-)

diff --git a/Documentation/trace/workqueue.txt b/Documentation/trace/workqueue.txt
new file mode 100644
index 0000000..4019a8a
--- /dev/null
+++ b/Documentation/trace/workqueue.txt
@@ -0,0 +1,114 @@
+The workqueue tracer is a tool that can provide informations
+about worklets execution frequency, latency and worklets/workqueues
+lifecycle.
+
+== A statistical/histogram tracer ==
+
+This tracer provides a snapshot of the workqueues and worklets
+current state.
+
+Eg:
+
+# CPU INSERTED EXECUTED MAX us AVG us TASKNAME:PID
+# | | | | ` | -WORKFUNC
+# | | | | | |
+ 0 5903 5977 events/0:9
+ 0 1 1 38 38 |-hpet_work
+ 0 49 48 295 224 |-rt_worker_func
+ 0 2934 2933 73 11 |-vmstat_update
+ 0 935 935 13143 264 |-console_callback
+ 0 80 80 1634632587 45804402 |-test_work
+ 0 10 9 239 85 |-rekey_seq_generator
+ 0 10 10 0 0 |-lru_add_drain_per_cpu
+ 0 1 1 4 4 |-sync_cmos_clock
+ 0 651 651 366 65 |-flush_to_ldisc
+ 0 1105 1105 13171 256 |-fb_flashcursor
+ 0 127 120 213 18 `-dst_gc_task
+ 0 0 0 cpuset:11
+ 0 1409 1409 khelper:12
+ 0 1409 1409 124030 754 `-__call_usermodehelper
+ 0 0 0 kintegrityd/0:174
+ 0 5823 5823 kblockd/0:179
+ 0 336 336 176 40 |-blk_unplug_work
+ 0 5487 5487 141 21 `-cfq_kick_queue
+ 0 0 0 kacpid:186
+ 0 0 0 kacpi_notify:187
+ 0 0 0 tifm:498
+ 0 19505 19505 ata/0:508
+ 0 19505 19505 114 24 `-ata_pio_task
+ 0 0 0 ata_aux:511
+ 0 0 0 aio/0:871
+ 0 0 0 crypto/0:897
+ 0 0 0 scsi_tgtd/0:2368
+ 0 0 0 iscsi_eh:2386
+ 0 0 0 kpsmoused:2525
+ 0 0 0 hd-audio0:2714
+ 0 0 0 krxrpcd/0:2752
+ 0 242 242 reiserfs/0:2896
+ 0 242 242 4563280 21918 `-flush_async_commits
+ 1 0 0 reiserfs/1:6438
+ 1 0 0 krxrpcd/1:6439
+ 1 0 0 scsi_tgtd/1:6440
+ 1 0 0 crypto/1:6441
+ 1 0 0 aio/1:6442
+ 1 62 62 ata/1:6443
+ 1 62 62 28 24 `-ata_pio_task
+ 1 9 9 kblockd/1:6444
+ 1 9 9 102 54 `-blk_unplug_work
+ 1 0 0 kintegrityd/1:6445
+ 1 2544 2545 events/1:6446
+ 1 2541 2540 22 11 |-vmstat_update
+ 1 1 1 15 15 |-hpet_work
+ 1 2 2 10 6 `-lru_add_drain_per_cpu
+
+For each worklet, you can find how much it has been enqueued
+and executed. Also the MAX us and AVG us give you respectively
+the maximum and average time of execution in microseconds
+for a given worklet.
+
+A series of worklets is grouped under a workqueue using the
+following pattern:
+
+cpu_workqueue_thread[/cpu_nr]:pid
+|-work1
+|-work2
+...
+`-last_work
+
+If cpu_nr is not given, then the workqueue thread is
+a singlethread workqueue, bound to every possible cpu.
+
+Use the following commands to read a snapshot:
+
+mount -t debugfs debug /sys/kernel/debug/
+cat /sys/kernel/debug/tracing/trace_stat/workqueues
+
+
+== An event tracer ==
+
+The workqueue tracer also uses a set of events tracepoints which
+can be used to trace each key event from every workqueues or worklets.
+
+You can refer to Documentation/trace/events.txt for a detailed
+use of the events tracepoints. How to individually toggle them, how
+to use filters, which field is what, etc...
+
+For a simple capture of all workqueues events:
+
+# mount -t debugfs debug /sys/kernel/debug/
+# cd /sys/kernel/debug/tracing/events/workqueue
+# ls
+filter worklet_complete worklet_enqueue_delayed workqueue_creation workqueue_flush
+worklet_cancel worklet_enqueue worklet_execute workqueue_destruction
+# for e in $(ls); do echo 1 > $e/enable; done
+# cat /sys/kernel/debug/tracing/trace
+
+ #
+ # TASK-PID CPU# TIMESTAMP FUNCTION
+ # | | | | |
+
+<...>-5627 [000] 4597.858645: worklet_enqueue: thread=ata/0:508 func=ata_pio_task+0x0/0x280 cpu=0
+<...>-508 [000] 4597.858660: worklet_execute: thread=ata/0:508 work=ffff88007e9e67b8 func=ata_pio_task+0x0/0x280
+<...>-508 [000] 4597.858684: worklet_complete: thread=ata/0:508 work=ffff88007e9e67b8
+<...>-2437 [000] 4597.861259: worklet_cancel: func=ata_pio_task+0x0/0x280
+[...]
--
1.6.2.3


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