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summarize

Summarize is a tool to produce a human readable summary of measureme profiling data.

Installing summarize

To use this tool you will first want to install it:

cargo install --git https://github.com/rust-lang/measureme --branch stable summarize

Profiling the nightly compiler

To profile the nightly compiler first ensure that you have a recent nightly compiler by typing rustup update nightly. If your compiler version is older than 2019-04-13 the profiling feature has not yet been added.

Profiling the compiler is done by passing the flag -Z self-profile to rustc. Note that -Z flags are unstable, so you must use the nightly compiler. As an example we will profile the regex crate.

git clone https://github.com/rust-lang/regex.git
cd regex
cargo +nightly rustc -- -Z self-profile

The commands above will run rustc with the flag that enables profiling. You should now have a file in your directory named regex-{pid}.mm_profdata which contains the profiler data. (If you got three files instead, you will need to use an older version of the summarize tool such as the 0.7.1 release to read the data: cargo install --git https://github.com/rust-lang/measureme --tag 0.7.1 summarize)

You can now use the summarize tool we installed in the previous section to view the contents of these files:

summarize summarize regex-{pid}.mm_profdata
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | Item                   | Self time | % of total time | Item count | Cache hits | Blocked time | Incremental load time |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | LLVM_emit_obj          | 4.51s     | 41.432          | 141        | 0          | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | LLVM_module_passes     | 1.05s     | 9.626           | 140        | 0          | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | LLVM_make_bitcode      | 712.94ms  | 6.543           | 140        | 0          | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | typeck_tables_of       | 542.23ms  | 4.976           | 17470      | 16520      | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | codegen                | 366.82ms  | 3.366           | 141        | 0          | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | optimized_mir          | 188.22ms  | 1.727           | 11668      | 9114       | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | mir_built              | 156.30ms  | 1.434           | 2040       | 1020       | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | evaluate_obligation    | 151.95ms  | 1.394           | 33134      | 23817      | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | LLVM_compress_bitcode  | 126.55ms  | 1.161           | 140        | 0          | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | codegen crate          | 119.08ms  | 1.093           | 1          | 0          | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | mir_const              | 117.82ms  | 1.081           | 1050       | 30         | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
#
# (rows elided)
#
# Total cpu time: 10.896488447s

Profiling your own build of rustc

You can also profile your own custom build of rustc. First you'll have to clone the rust repo and compile it. You can find the full guide on doing this here, but if you've never built rustc before, we suggest starting with

git clone https://github.com/rust-lang/rust.git
./x.py build
# This will take a while...
rustup toolchain link mytoolchain build/x86_64-unknown-linux-gnu/stage1

Where mytoolchain is the name of your custom toolchain. Now we do more or less the same as before: (with regex as example)

git clone https://github.com/rust-lang/regex.git
cd regex
cargo +mytoolchain rustc -- -Z self-profile
summarize summarize regex-{pid}.mm_profdata
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | Item                   | Self time | % of total time | Item count | Cache hits | Blocked time | Incremental load time |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | LLVM_emit_obj          | 4.51s     | 41.432          | 141        | 0          | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | LLVM_module_passes     | 1.05s     | 9.626           | 140        | 0          | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | LLVM_make_bitcode      | 712.94ms  | 6.543           | 140        | 0          | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | typeck_tables_of       | 542.23ms  | 4.976           | 17470      | 16520      | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | codegen                | 366.82ms  | 3.366           | 141        | 0          | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | optimized_mir          | 188.22ms  | 1.727           | 11668      | 9114       | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
# | mir_built              | 156.30ms  | 1.434           | 2040       | 1020       | 0.00ns       | 0.00ns                |
# +------------------------+-----------+-----------------+------------+------------+--------------+-----------------------+
#
# (rows elided)
#
# Total cpu time: 10.896488447s

Note that your custom build of the compiler must not use a newer version of the measureme library than the one used in the summarize tool.

Reading the output

The table is a list of different events. Each event has its own row, and the columns summarize the information for that event.

  • The Item column contains the name of the event.
  • The Self time column contains the total time used by events of this type.
  • The % of total time column contains how large a percentage Self time is of the total runtime of the compiler.
  • The Item count column describes the number of times that event has occurred.
  • The Cache hits column displays the number of times a query was found in the cache.
  • The Blocked time is the amount of time this event spent while waiting on a different thread. (This only happens with parallel queries enabled)
  • The Incremental load time is the time spent loading the result of a query from a previous incremental build. This is analogous to Cache hits.

The table is sorted by Self time descending.

The diff sub command

The diff sub command allows you to compare the performance of two different profiles by event.

The output is a table like that of the summarize sub command but it instead shows the differences in each metric.

summarize diff base-profile.mm_profdata changed-profile.mm_profdata
# +---------------------------+--------------+------------+------------+--------------+-----------------------+
# | Item                      | Self Time    | Item count | Cache hits | Blocked time | Incremental load time |
# +---------------------------+--------------+------------+------------+--------------+-----------------------+
# | LLVM_module_passes        | -66.626471ms | +0         | +0         | +0ns         | +0ns                  |
# +---------------------------+--------------+------------+------------+--------------+-----------------------+
# | LLVM_emit_obj             | -38.700719ms | +0         | +0         | +0ns         | +0ns                  |
# +---------------------------+--------------+------------+------------+--------------+-----------------------+
# | LLVM_make_bitcode         | +32.006706ms | +0         | +0         | +0ns         | +0ns                  |
# +---------------------------+--------------+------------+------------+--------------+-----------------------+
# | mir_borrowck              | -12.808322ms | +0         | +0         | +0ns         | +0ns                  |
# +---------------------------+--------------+------------+------------+--------------+-----------------------+
# | typeck_tables_of          | -10.325247ms | +0         | +0         | +0ns         | +0ns                  |
# +---------------------------+--------------+------------+------------+--------------+-----------------------+
# (rows elided)
# Total cpu time: -155.177548ms

The table is sorted by the absolute value of Self time descending.