view rust/hgcli/.cargo/config @ 47120:7109a38830c9

dirstate-tree: Fold "tracked descendants" counter update in main walk

For the purpose of implementing `has_tracked_dir` (which means "has tracked
descendants) without an expensive sub-tree traversal, we maintaing a counter
of tracked descendants on each "directory" node of the tree-shaped dirstate.

Before this changeset, mutating or inserting a node at a given path would
involve:

* Walking the tree from root through ancestors to find the node or the spot
  where to insert it
* Looking at the previous node if any to decide what counter update is needed
* Performing any node mutation
* Walking the tree *again* to update counters in ancestor nodes

When profiling `hg status` on a large repo, this second walk takes times
while loading a the dirstate from disk.

It turns out we have enough information to decide before he first tree walk
what counter update is needed. This changeset merges the two walks, gaining
~10% of the total time for `hg update` (in the same hyperfine benchmark as
the previous changeset).

---

Profiling was done by compiling with this `.cargo/config`:

    [profile.release]
    debug = true

then running with:

    py-spy record -r 500 -n -o /tmp/hg.json --format speedscope -- \
    ./hg status -R $REPO --config experimental.dirstate-tree.in-memory=1

then visualizing the recorded JSON file in https://www.speedscope.app/

Differential Revision: https://phab.mercurial-scm.org/D10554

# By default Rust will not export dynamic symbols from built executables.
# Python symbols need to be exported from executables in order for that
# executable to load Python extension modules, which are shared libraries.
# Otherwise, the extension module / shared library is unable to resolve
# Python symbols. This file contains target-specific configuration
# overrides to export dynamic symbols from executables.
#
# Ideally we would achieve this functionality via the build.rs build
# script. But custom compiler flags via build scripts apparently only
# support limited options.

[target.x86_64-unknown-linux-gnu]
rustflags = ["-C", "link-args=-Wl,-export-dynamic"]