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Differential D8603

rust: add a pointer for profiling to the README
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Authored by valentin.gatienbaron on May 30 2020, 12:56 PM.

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rHG7ca1d635e4a6: rust: add a pointer for profiling to the README
Summary

As figuring out how to get useful profiles is not obvious.

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valentin.gatienbaron added a commit: rHG7ca1d635e4a6: rust: add a pointer for profiling to the README.Jun 1 2020, 11:48 AM
This revision was not accepted when it landed; it landed in state Needs Review.
Closed by commit rHG7ca1d635e4a6: rust: add a pointer for profiling to the README (authored by valentin.gatienbaron). · Explain Why
This revision was automatically updated to reflect the committed changes.

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Mrust/README.rst (15 lines)

Diff 21538

rust/README.rst

checking module policy (rust+c-allow) checking module policy (rust+c-allow)
If the environment variable ``HGWITHRUSTEXT=cpython`` is set, the Rust If the environment variable ``HGWITHRUSTEXT=cpython`` is set, the Rust
extension will be used by default unless ``--no-rust``. extension will be used by default unless ``--no-rust``.
One day we may use this environment variable to switch to new experimental One day we may use this environment variable to switch to new experimental
binding crates like a hypothetical ``HGWITHRUSTEXT=hpy``. binding crates like a hypothetical ``HGWITHRUSTEXT=hpy``.
Profiling
=========
Setting the environment variable ``RUST_LOG=trace`` will make hg print
a few high level rust-related performance numbers. It can also
indicate why the rust code cannot be used (say, using lookarounds in
hgignore).
``py-spy`` (https://github.com/benfred/py-spy) can be used to
construct a single profile with rust functions and python functions
(as opposed to ``hg --profile``, which attributes time spent in rust
to some unlucky python code running shortly after the rust code, and
as opposed to tools for native code like ``perf``, which attribute
time to the python interpreter instead of python functions).
Developing Rust Developing Rust
=============== ===============
The current version of Rust in use is ``1.34.2``, because it's what Debian The current version of Rust in use is ``1.34.2``, because it's what Debian
stable has. You can use ``rustup override set 1.34.2`` at the root of the repo stable has. You can use ``rustup override set 1.34.2`` at the root of the repo
to make it easier on you. to make it easier on you.
Go to the ``hg-cpython`` folder:: Go to the ``hg-cpython`` folder::