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