Flame Graphs visualize profiled code

Main Website: http://www.brendangregg.com/flamegraphs.html

Example (click to zoom):

Other sites:

• The Flame Graph article in ACMQ and CACM: http://queue.acm.org/detail.cfm?id=2927301 http://cacm.acm.org/magazines/2016/6/202665-the-flame-graph/abstract
• CPU profiling using Linux perf_events, DTrace, SystemTap, or ktap: http://www.brendangregg.com/FlameGraphs/cpuflamegraphs.html
• CPU profiling using XCode Instruments: http://schani.wordpress.com/2012/11/16/flame-graphs-for-instruments/
• CPU profiling using Xperf.exe: http://randomascii.wordpress.com/2013/03/26/summarizing-xperf-cpu-usage-with-flame-graphs/
• Memory profiling: http://www.brendangregg.com/FlameGraphs/memoryflamegraphs.html
• Other examples, updates, and news: http://www.brendangregg.com/flamegraphs.html#Updates

Flame graphs can be created in three steps:

1. Capture stacks

2. Fold stacks

3. flamegraph.pl

4. Capture stacks ================= Stack samples can be captured using Linux perf_events, FreeBSD pmcstat (hwpmc), DTrace, SystemTap, and many other profilers. See the stackcollapse-* converters.

Linux perf_events

Using Linux perf_events (aka "perf") to capture 60 seconds of 99 Hertz stack samples, both user- and kernel-level stacks, all processes:

# perf record -F 99 -a -g -- sleep 60
# perf script > out.perf

Now only capturing PID 181:

# perf record -F 99 -p 181 -g -- sleep 60
# perf script > out.perf

DTrace

Using DTrace to capture 60 seconds of kernel stacks at 997 Hertz:

# dtrace -x stackframes=100 -n 'profile-997 /arg0/ { @[stack()] = count(); } tick-60s { exit(0); }' -o out.kern_stacks

Using DTrace to capture 60 seconds of user-level stacks for PID 12345 at 97 Hertz:

# dtrace -x ustackframes=100 -n 'profile-97 /pid == 12345 && arg1/ { @[ustack()] = count(); } tick-60s { exit(0); }' -o out.user_stacks

60 seconds of user-level stacks, including time spent in-kernel, for PID 12345 at 97 Hertz:

# dtrace -x ustackframes=100 -n 'profile-97 /pid == 12345/ { @[ustack()] = count(); } tick-60s { exit(0); }' -o out.user_stacks

Switch ustack() for jstack() if the application has a ustack helper to include translated frames (eg, node.js frames; see: http://dtrace.org/blogs/dap/2012/01/05/where-does-your-node-program-spend-its-time/). The rate for user-level stack collection is deliberately slower than kernel, which is especially important when using jstack() as it performs additional work to translate frames.

2. Fold stacks ============== Use the stackcollapse programs to fold stack samples into single lines. The programs provided are:

• stackcollapse.pl: for DTrace stacks
• stackcollapse-perf.pl: for Linux perf_events "perf script" output
• stackcollapse-pmc.pl: for FreeBSD pmcstat -G stacks
• stackcollapse-stap.pl: for SystemTap stacks
• stackcollapse-instruments.pl: for XCode Instruments
• stackcollapse-vtune.pl: for Intel VTune profiles
• stackcollapse-ljp.awk: for Lightweight Java Profiler
• stackcollapse-jstack.pl: for Java jstack(1) output
• stackcollapse-gdb.pl: for gdb(1) stacks

Usage example:

For perf_events:
$ ./stackcollapse-perf.pl out.perf > out.folded

For DTrace:
$ ./stackcollapse.pl out.kern_stacks > out.kern_folded

The output looks like this:

unix`_sys_sysenter_post_swapgs 1401
unix`_sys_sysenter_post_swapgs;genunix`close 5
unix`_sys_sysenter_post_swapgs;genunix`close;genunix`closeandsetf 85
unix`_sys_sysenter_post_swapgs;genunix`close;genunix`closeandsetf;c2audit`audit_closef 26
unix`_sys_sysenter_post_swapgs;genunix`close;genunix`closeandsetf;c2audit`audit_setf 5
unix`_sys_sysenter_post_swapgs;genunix`close;genunix`closeandsetf;genunix`audit_getstate 6
unix`_sys_sysenter_post_swapgs;genunix`close;genunix`closeandsetf;genunix`audit_unfalloc 2
unix`_sys_sysenter_post_swapgs;genunix`close;genunix`closeandsetf;genunix`closef 48
[...]

3. flamegraph.pl ================ Use flamegraph.pl to render a SVG.

$ ./flamegraph.pl out.kern_folded > kernel.svg

An advantage of having the folded input file (and why this is separate to flamegraph.pl) is that you can use grep for functions of interest. Eg:

$ grep cpuid out.kern_folded | ./flamegraph.pl > cpuid.svg

Provided Examples

Linux perf_events

An example output from Linux "perf script" is included, gzip'd, as example-perf-stacks.txt.gz. The resulting flame graph is example-perf.svg:

You can create this using:

$ gunzip -c example-perf-stacks.txt.gz | ./stackcollapse-perf.pl --kernel | ./flamegraph.pl --color=java --hash > example-perf.svg

This shows my typical workflow: I'll gzip profiles on the target, then copy them to my laptop for analysis. Since I have hundreds of profiles, I leave them gzip'd!

Since this profile included Java, I used the flamegraph.pl --color=java palette. I've also used stackcollapse-perf.pl --kernel, which allows a separate color to be used for kernel code. The resulting flame graph uses: green == Java, yellow == C++, red == user-mode native, orange == kernel.

This profile was from an analysis of vert.x performance. The benchmark client, wrk, is also visible in the flame graph.

DTrace

An example output from DTrace is also included, example-dtrace-stacks.txt, and the resulting flame graph, example-dtrace.svg:

You can generate this using:

$ ./stackcollapse.pl example-stacks.txt | ./flamegraph.pl > example.svg

This was from a particular performance investigation: the Flame Graph identified that CPU time was spent in the lofs module, and quantified that time.

Options

See the USAGE message (--help) for options:

USAGE: ./flamegraph.pl [options] infile > outfile.svg

--title       # change title text
--width       # width of image (default 1200)
--height      # height of each frame (default 16)
--minwidth    # omit smaller functions (default 0.1 pixels)
--fonttype    # font type (default "Verdana")
--fontsize    # font size (default 12)
--countname   # count type label (default "samples")
--nametype    # name type label (default "Function:")
--colors      # set color palette. choices are: hot (default), mem, io,
              # wakeup, chain, java, js, perl, red, green, blue, aqua,
              # yellow, purple, orange
--hash        # colors are keyed by function name hash
--cp          # use consistent palette (palette.map)
--reverse     # generate stack-reversed flame graph
--inverted    # icicle graph
--negate      # switch differential hues (blue<->red)
--help        # this message

eg,
./flamegraph.pl --title="Flame Graph: malloc()" trace.txt > graph.svg

As suggested in the example, flame graphs can process traces of any event, such as malloc()s, provided stack traces are gathered.

Consistent Palette

If you use the --cp option, it will use the $colors selection and randomly generate the palette like normal. Any future flamegraphs created using the --cp option will use the same palette map. Any new symbols from future flamegraphs will have their colors randomly generated using the $colors selection.

If you don't like the palette, just delete the palette.map file.

This allows your to change your colorscheme between flamegraphs to make the differences REALLY stand out.

Example:

Say we have 2 captures, one with a problem, and one when it was working (whatever "it" is):

cat working.folded | ./flamegraph.pl --cp > working.svg
# this generates a palette.map, as per the normal random generated look.

cat broken.folded | ./flamegraph.pl --cp --colors mem > broken.svg
# this svg will use the same palette.map for the same events, but a very
# different colorscheme for any new events.

Take a look at the demo directory for an example:

palette-example-working.svg
palette-example-broken.svg