Commit b41df645 authored by Randy Dunlap's avatar Randy Dunlap Committed by Ingo Molnar
Browse files

Documentation: Update tracepoint-analysis.txt



Fix grammar, spelling, punctuation, hyphenation, section
numbering. Tell what PCL means.
Signed-off-by: default avatarRandy Dunlap <randy.dunlap@oracle.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4B2C0D70.4030707@oracle.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 360b6e5c
......@@ -10,8 +10,8 @@ Tracepoints (see Documentation/trace/tracepoints.txt) can be used without
creating custom kernel modules to register probe functions using the event
tracing infrastructure.
Simplistically, tracepoints will represent an important event that when can
be taken in conjunction with other tracepoints to build a "Big Picture" of
Simplistically, tracepoints represent important events that can be
taken in conjunction with other tracepoints to build a "Big Picture" of
what is going on within the system. There are a large number of methods for
gathering and interpreting these events. Lacking any current Best Practises,
this document describes some of the methods that can be used.
......@@ -33,12 +33,12 @@ calling
will give a fair indication of the number of events available.
2.2 PCL
2.2 PCL (Performance Counters for Linux)
-------
Discovery and enumeration of all counters and events, including tracepoints
Discovery and enumeration of all counters and events, including tracepoints,
are available with the perf tool. Getting a list of available events is a
simple case of
simple case of:
$ perf list 2>&1 | grep Tracepoint
ext4:ext4_free_inode [Tracepoint event]
......@@ -49,19 +49,19 @@ simple case of
[ .... remaining output snipped .... ]
2. Enabling Events
3. Enabling Events
==================
2.1 System-Wide Event Enabling
3.1 System-Wide Event Enabling
------------------------------
See Documentation/trace/events.txt for a proper description on how events
can be enabled system-wide. A short example of enabling all events related
to page allocation would look something like
to page allocation would look something like:
$ for i in `find /sys/kernel/debug/tracing/events -name "enable" | grep mm_`; do echo 1 > $i; done
2.2 System-Wide Event Enabling with SystemTap
3.2 System-Wide Event Enabling with SystemTap
---------------------------------------------
In SystemTap, tracepoints are accessible using the kernel.trace() function
......@@ -86,7 +86,7 @@ were allocating the pages.
print_count()
}
2.3 System-Wide Event Enabling with PCL
3.3 System-Wide Event Enabling with PCL
---------------------------------------
By specifying the -a switch and analysing sleep, the system-wide events
......@@ -107,16 +107,16 @@ for a duration of time can be examined.
Similarly, one could execute a shell and exit it as desired to get a report
at that point.
2.4 Local Event Enabling
3.4 Local Event Enabling
------------------------
Documentation/trace/ftrace.txt describes how to enable events on a per-thread
basis using set_ftrace_pid.
2.5 Local Event Enablement with PCL
3.5 Local Event Enablement with PCL
-----------------------------------
Events can be activate and tracked for the duration of a process on a local
Events can be activated and tracked for the duration of a process on a local
basis using PCL such as follows.
$ perf stat -e kmem:mm_page_alloc -e kmem:mm_page_free_direct \
......@@ -131,18 +131,18 @@ basis using PCL such as follows.
0.973913387 seconds time elapsed
3. Event Filtering
4. Event Filtering
==================
Documentation/trace/ftrace.txt covers in-depth how to filter events in
ftrace. Obviously using grep and awk of trace_pipe is an option as well
as any script reading trace_pipe.
4. Analysing Event Variances with PCL
5. Analysing Event Variances with PCL
=====================================
Any workload can exhibit variances between runs and it can be important
to know what the standard deviation in. By and large, this is left to the
to know what the standard deviation is. By and large, this is left to the
performance analyst to do it by hand. In the event that the discrete event
occurrences are useful to the performance analyst, then perf can be used.
......@@ -166,7 +166,7 @@ In the event that some higher-level event is required that depends on some
aggregation of discrete events, then a script would need to be developed.
Using --repeat, it is also possible to view how events are fluctuating over
time on a system wide basis using -a and sleep.
time on a system-wide basis using -a and sleep.
$ perf stat -e kmem:mm_page_alloc -e kmem:mm_page_free_direct \
-e kmem:mm_pagevec_free \
......@@ -180,7 +180,7 @@ time on a system wide basis using -a and sleep.
1.002251757 seconds time elapsed ( +- 0.005% )
5. Higher-Level Analysis with Helper Scripts
6. Higher-Level Analysis with Helper Scripts
============================================
When events are enabled the events that are triggering can be read from
......@@ -190,11 +190,11 @@ be gathered on-line as appropriate. Examples of post-processing might include
o Reading information from /proc for the PID that triggered the event
o Deriving a higher-level event from a series of lower-level events.
o Calculate latencies between two events
o Calculating latencies between two events
Documentation/trace/postprocess/trace-pagealloc-postprocess.pl is an example
script that can read trace_pipe from STDIN or a copy of a trace. When used
on-line, it can be interrupted once to generate a report without existing
on-line, it can be interrupted once to generate a report without exiting
and twice to exit.
Simplistically, the script just reads STDIN and counts up events but it
......@@ -212,12 +212,12 @@ also can do more such as
processes, the parent process responsible for creating all the helpers
can be identified
6. Lower-Level Analysis with PCL
7. Lower-Level Analysis with PCL
================================
There may also be a requirement to identify what functions with a program
There may also be a requirement to identify what functions within a program
were generating events within the kernel. To begin this sort of analysis, the
data must be recorded. At the time of writing, this required root
data must be recorded. At the time of writing, this required root:
$ perf record -c 1 \
-e kmem:mm_page_alloc -e kmem:mm_page_free_direct \
......@@ -253,11 +253,11 @@ perf report.
# (For more details, try: perf report --sort comm,dso,symbol)
#
According to this, the vast majority of events occured triggered on events
within the VDSO. With simple binaries, this will often be the case so lets
According to this, the vast majority of events triggered on events
within the VDSO. With simple binaries, this will often be the case so let's
take a slightly different example. In the course of writing this, it was
noticed that X was generating an insane amount of page allocations so lets look
at it
noticed that X was generating an insane amount of page allocations so let's look
at it:
$ perf record -c 1 -f \
-e kmem:mm_page_alloc -e kmem:mm_page_free_direct \
......@@ -280,8 +280,8 @@ This was interrupted after a few seconds and
# (For more details, try: perf report --sort comm,dso,symbol)
#
So, almost half of the events are occuring in a library. To get an idea which
symbol.
So, almost half of the events are occurring in a library. To get an idea which
symbol:
$ perf report --sort comm,dso,symbol
# Samples: 27666
......@@ -297,7 +297,7 @@ symbol.
0.01% Xorg /opt/gfx-test/lib/libpixman-1.so.0.13.1 [.] get_fast_path
0.00% Xorg [kernel] [k] ftrace_trace_userstack
To see where within the function pixmanFillsse2 things are going wrong
To see where within the function pixmanFillsse2 things are going wrong:
$ perf annotate pixmanFillsse2
[ ... ]
......
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