Ocfs2 devel - Sep 2009 - [PATCH 0/2] ocfs2: add trace event support for ocfs2

following patches add trace event support for ocfs2.
for tracepoint, see Documentation/trace/tracepoints.txt
for trace events, see Documentation/trace/events.txt

the first patch add file include/trace/events/ocfs2.h to kernel tree. it is used
to store trace declarations. it's contents are self-explained.
NOTE that each ocfs2 header file should be above "#include
<linux/tracepoint.h>"

the second one is an example which adds trace event to ocfs2_file_aio_read().
NOTE that CREATE_TRACE_POINTS must be defined before including
trace/event/ocfs2.h
when trace event is used.

enable/disable the trace event:
1) debugfs is need to be mount for using trace event.
	mount -t debugfs debugfs /sys/kernel/debug(or somewhere else)
2) enable/disable some specific event,
	echo
'1'/'0'>/sys/kernel/debug/tracing/events/ocfs2/ocfs2_file_aio_read/enable
3) to see the trace log,
	cat /sys/kernel/debug/tracing/trace

an output example is:
[root at cool ocfs2_file_aio_read]# cat /sys/kernel/debug/tracing/trace
# tracer: nop                                      
#                                                  
#           TASK-PID    CPU#    TIMESTAMP  FUNCTION
#              | |       |          |         |    
             cat-2587  [001]   708.929889: ocfs2_file_aio_read: 0xf544bed8
0xf544bf5c 1 0

             cat-2587  [000]   708.944128: ocfs2_file_aio_read: 0xf544bed8
0xf544bf5c 1 43

examples of using filter.
1) if pid is 0, do the trace:
	echo "common_pid == 0"
>/sys/kernel/debug/tracing/events/ocfs2/ocfs2_file_aio_read/filter
2) if group id not 0, do the trace:
	echo "common_tgid != 0" >filter

for filter expression, so far, see
http://article.gmane.org/gmane.linux.kernel/887690?

Wengang Wang wrote:
> following patches add trace event support for ocfs2.
> for tracepoint, see Documentation/trace/tracepoints.txt
> for trace events, see Documentation/trace/events.txt
> 
> the first patch add file include/trace/events/ocfs2.h to kernel tree. it is
used
> to store trace declarations. it's contents are self-explained.
> NOTE that each ocfs2 header file should be above "#include
<linux/tracepoint.h>"
> 
> the second one is an example which adds trace event to
ocfs2_file_aio_read().
> NOTE that CREATE_TRACE_POINTS must be defined before including
trace/event/ocfs2.h
> when trace event is used.
and CREATE_TRACE_POINTS should be defined in only one .c file please.

regards,
wengang.
> 
> enable/disable the trace event:
> 1) debugfs is need to be mount for using trace event.
> 	mount -t debugfs debugfs /sys/kernel/debug(or somewhere else)
> 2) enable/disable some specific event,
> 	echo
'1'/'0'>/sys/kernel/debug/tracing/events/ocfs2/ocfs2_file_aio_read/enable
> 3) to see the trace log,
> 	cat /sys/kernel/debug/tracing/trace
> 
> an output example is:
> [root at cool ocfs2_file_aio_read]# cat /sys/kernel/debug/tracing/trace
> # tracer: nop                                      
> #                                                  
> #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
> #              | |       |          |         |    
>              cat-2587  [001]   708.929889: ocfs2_file_aio_read: 0xf544bed8
0xf544bf5c 1 0
> 
>              cat-2587  [000]   708.944128: ocfs2_file_aio_read: 0xf544bed8
0xf544bf5c 1 43
> 
> examples of using filter.
> 1) if pid is 0, do the trace:
> 	echo "common_pid == 0"
>/sys/kernel/debug/tracing/events/ocfs2/ocfs2_file_aio_read/filter
> 2) if group id not 0, do the trace:
> 	echo "common_tgid != 0" >filter
> 
> for filter expression, so far, see
http://article.gmane.org/gmane.linux.kernel/887690?
> 
>

On Thu, Sep 17, 2009 at 06:19:44AM +0800, Wengang Wang
wrote:
> following patches add trace event support for ocfs2.
Wengang,
	This looks like a nice start.  Thank you for getting this going.
I'm sorry I haven't gotten back until now, I've been busy.
	What I'd like to do next is get a small starting set of
tracepoints.  You have one tracepoint in this patch as a good example,
but we should get a few more.  I don't want every mlog changed into a
tracepoint.  Some of them are old and useless :-)  Instead, I'd like to
find information we often want while debugging.
	Tao, Tiger, and Sunil, what are parts of the code you often come
across when debugging?  Certain mlog() prints you always find really
important to see.  If you point them out, Wengang can cook up
tracepoints for them.

Joel

-- 

"But all my words come back to me
 In shades of mediocrity.
 Like emptiness in harmony
 I need someone to comfort me."

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127