The previous system of relying on test name prefixes for ordering was
simple, but organizing tests by dependencies and topologically sorting
during compilation is 1. more flexible and 2. simplifies test names,
which get typed a lot.
Note these are not "hard" dependencies, each test suite should work fine
in isolation. These "after" dependencies just hint an ordering when all
tests are ran.
As such, it's worth noting the tests should NOT error of a dependency is
missing. This unfortunately makes it a bit hard to catch typos, but
allows faster compilation of a subset of tests.
---
To make this work the way tests are linked has changed from using custom
linker section (fun linker magic!) to a weakly linked array appended to
every source file (also fun linker magic!).
At least with this method test.py has strict control over the test
ordering, and doesn't depend on 1. the order in which the linker merges
sections, and 2. the order tests are passed to test.py. I didn't realize
the previous system was so fragile.
It doesn't make sense to test more complex logic, such as t2_btree.toml,
when the logic it is built on, t1_rbyd.toml, does not past testing. The
test runner already guarantees a consistent lexicographic order, so all
we need to do is renamed these from test_* -> tn_*.
Note, if we every have more than 10 tests, we will need to bump up the
number of digits for all tests, so t1_rbyd.toml -> t01_rbyd.toml. This
is the main downside of lexicographic ordering. But we'll cross that
bridge when we get to it.
Validating btree nodes during lfsr_btree_lookup was useful as a
proof-of-concept, but it's not really needed if we validate btree nodes
during mtree traversal.
mtree traversal provides the first reads into the filesystem. It's how
we find the real mroot, and (in theory at the moment) it provides the core
operation for error detection in correction. With this in mind,
implementing btree node validation in mtree traversal makes a lot of
sense, with lfsr_btree_lookup leveraging an assumed successful
validation for faster/smaller btree walks.
Note that btree node validation during traversal is still optional. We
really don't want to pay this cost during block allocation for example.
---
It may look concerning that there's no related validation in btree traversal
layer itself.
It turns out that a quirk of btree traversal returning inner btree nodes on
first visit, before actually traversing the btree node, is that it's
safe for us to validte the btree node in only the mtree traversal layer.
As long as we don't continue traversing on finding a corrupted btree,
the btree traversal layer will never traverse an unvalidated btree node.
This keeps all the validation logic in the same place, mtree traversal.
I don't know if this will stay this way if/when more error correction
features are added, but it's convenient in the meantime.
These benchmarks are now more useful for seeing how these B-trees perform.
In plot.py/plotmpl.py:
- Added --legend as another alias for -l, --legend-right.
- Allowed omitting of datasets from the legend by using empty strings
in --labels.
- Do not sum multiple data points on the same x coordinate. This was a
bad idea that risks invalid results going unnoticed.
As a plus multiple data points on the same x coordinate can be abused for
a cheap representation of measurement error.
Christopher Haster