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Restore old initial batch distribution logic in LoadScheduling (#812)

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* Restore old initial batch distribution logic in LoadScheduling

pytest orders tests for optimal sequential execution - i. e. avoiding
unnecessary setup and teardown of fixtures. So executing tests in consecutive
chunks is important for optimal performance.

Commit 09d79ace35 optimized test distribution for
the corner case, when the number of tests is less than 2 * number of nodes.
At the same time, it made initial test distribution worse for all other cases.
If some tests use some fixture, and these tests fit into the initial batch,
the fixture will be created min(n_tests, n_workers) times, no matter how many
other tests there are. With the old algorithm (before
09d79ace35), if there are enough tests not using
the fixture, the fixture was created only once.

So restore the old behavior for typical cases where the number of tests is
much greater than the number of workers (or, strictly speaking, when there
are at least 2 tests for every node).

In my test suite, where fixtures create Docker containers, this change reduces
total run time by 10-15%.

This is a partial revert of commit 09d79ace35

Co-authored-by: Bruno Oliveira <nicoddemus@gmail.com>
This commit is contained in:
Aleksandr Mezin
2022-10-22 16:12:16 +06:00
committed by GitHub
parent a1785b539c
commit 80130d59ea
3 changed files with 48 additions and 12 deletions
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Partially restore old initial batch distribution algorithm in ``LoadScheduling``.
pytest orders tests for optimal sequential execution - i. e. avoiding
unnecessary setup and teardown of fixtures. So executing tests in consecutive
chunks is important for optimal performance.
In v1.14, initial test distribution in ``LoadScheduling`` was changed to
round-robin, optimized for the corner case, when the number of tests is less
than ``2 * number of nodes``. At the same time, it became worse for all other
cases.
For example: if some tests use some "heavy" fixture, and these tests fit into
the initial batch, with round-robin distribution the fixture will be created
``min(n_tests, n_workers)`` times, no matter how many other tests there are.
With the old algorithm (before v1.14), if there are enough tests not using
the fixture, the fixture was created only once.
So restore the old behavior for typical cases where the number of tests is
much greater than the number of workers (or, strictly speaking, when there
are at least 2 tests for every node).