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improved doc/HelpfulTools.md on profiling Tor

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(Based on join work at https://pad.riseup.net/p/profiling-tor)
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Pierre-Antoine Rault 2017-01-13 17:01:49 +01:00 committed by Nick Mathewson
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@ -142,6 +142,12 @@ run `make test-network`.
We also have scripts to run integration tests using Stem. To try them, set
`STEM_SOURCE_DIR` to your Stem source directory, and run `test-stem`.
Profiling Tor
-------------
Ongoing notes about Tor profiling can be found at
https://pad.riseup.net/p/profiling-tor
Profiling Tor with oprofile
---------------------------
@ -167,6 +173,55 @@ Here are some basic instructions
* `opcontrol --dump;`
* `opreport -l that_dir/*`
- Profit
Profiling Tor with perf
-----------------------
This works with a running Tor, and requires root.
1. Decide how long you want to profile for. Start with (say) 30 seconds. If that
works, try again with longer times.
2. Find the PID of your running tor process.
3. Run `perf record --call-graph dwarf -p <PID> sleep <SECONDS>`
(You may need to do this as root.)
You might need to add `-e cpu-clock` as an option to the perf record line
above, if you are on an older CPU without access to hardware profiling
events, or in a VM, or something.
4. Now you have a perf.data file. Have a look at it with `perf report
--no-children --sort symbol,dso` or `perf report --no-children --sort
symbol,dso --stdio --header`. How does it look?
5a. Once you have a nice big perf.data file, you can compress it, encrypt it,
and send it to your favorite Tor developers.
5b. Or maybe you'd rather not send a nice big perf.data file. Who knows what's
in that!? It's kinda scary. To generate a less scary file, you can use `perf
report -g > <FILENAME>.out`. Then you can compress that and put it somewhere
public.
Profiling Tor with gperftools aka Google-performance-tools
----------------------------------------------------------
This should work on nearly any unixy system. It doesn't seem to be compatible
with RunAsDaemon though.
Beforehand, install google-perftools.
1. You need to rebuild Tor, hack the linking steps to add `-lprofiler` to the
libs. You can do this by adding `LIBS=-lprofiler` when you call `./configure`.
Now you can run Tor with profiling enabled, and use the pprof utility to look at
performance! See the gperftools manual for more info, but basically:
2. Run `env CPUPROFILE=/tmp/profile src/or/tor -f <path/torrc>`. The profile file
is not written to until Tor finishes execuction.
3. Run `pprof src/or/tor /tm/profile` to start the REPL.
Generating and analyzing a callgraph
------------------------------------