The litmus benches are really only intended for introspection/debugging/
cool plots/etc. They're interesting to poke around with and cover a wide
range of littlefs's data-structures, but are not very rigorous.
To make this more clear for new users, added a new litmus flag for
benches:
litmus = true
This doesn't change anything about how the bench is run, but serves as a
marker to hint that the bench is intended for non-rigorous benchmarking.
---
In the makefile, litmus tests are disabled by default at runtime
(--no-litmus). This is to limit `make bench` to benches that are useful
for performance comparisons.
With --no-litmus at runtime, the litmus benches are at least compiled
into the bench_runner, which should hopefully encourage keeping them up
to date with code changes. Eventually we should also run them in CI, but
only to check for runtime errors.
Unlike our tests, we're not really worried about compile time at the
moment due to how few/small our benches are.
Based on some experience out-of-tree:
- bench_rbyd - Simple rbyd attr/id litmus benchmark
- bench_btree (new) - Simple btree id/name litmus benchmark
- bench_file (new) - Simple file read/write litmus benchmark
- bench_dir (new) - Simple dir read/write/stat litmus benchmark
- bench_wt - Heavy-duty write-throughput benchmark
- bench_rt (new) - Heavy-duty read-throughput benchmark
Benches take a long time to run for useful results, so we probably don't
want to go crazy with them like with the tests.
Honestly, we may want to chop this down to just the
write/read-throughput benches.
This is based on how bench.py/bench_runners have actually been used in
practice. The main changes have been to make the output of bench.py more
readibly consumable by plot.py/plotmpl.py without needing a bunch of
hacky intermediary scripts.
Now instead of a single per-bench BENCH_START/BENCH_STOP, benches can
have multiple named BENCH_START/BENCH_STOP invocations to measure
multiple things in one run:
BENCH_START("fetch", i, STEP);
lfsr_rbyd_fetch(&lfs, &rbyd_, rbyd.block, CFG->block_size) => 0;
BENCH_STOP("fetch");
Benches can also now report explicit results, for non-io measurements:
BENCH_RESULT("usage", i, STEP, rbyd.eoff);
The extra iter/size parameters to BENCH_START/BENCH_RESULT also allow
some extra information to be calculated post-bench. This infomation gets
tagged with an extra bench_agg field to help organize results in
plot.py/plotmpl.py:
- bench_meas=<meas>+amor, bench_agg=raw - amortized results
- bench_meas=<meas>+div, bench_agg=raw - per-byte results
- bench_meas=<meas>+avg, bench_agg=avg - average over BENCH_SEED
- bench_meas=<meas>+min, bench_agg=min - minimum over BENCH_SEED
- bench_meas=<meas>+max, bench_agg=max - maximum over BENCH_SEED
---
Also removed all bench.tomls for now. This may seem counterproductive in
a commit to improve benchmarking, but I'm not sure there's actual value
to keeping bench cases committed in tree.
These were alway quick to fall out of date (at the time of this commit
most of the low-level bench.tomls, rbyd, btree, etc, no longer
compiled), and most benchmarks were one-off collections of scripts/data
with results too large/cumbersome to commit and keep updated in tree.
I think the better way to approach benchmarking is a seperate repo
(multiple repos?) with all related scripts/state/code and results
committed into a hopefully reproducible snapshot. Keeping the
bench.tomls in that repo makes more sense in this model.
There may be some value to having benchmarks in CI in the future, but
for that to make sense they would need to actually fail on performance
regression. How to do that isn't so clear. Anyways we can always address
this in the future rather than now.
When you add a function to every benchmark suite, you know if should
probably be provided by the benchmark runner itself. That being said,
randomness in tests/benchmarks is a bit tricky because it needs to be
strictly controlled and reproducible.
No global state is used, allowing tests/benches to maintain multiple
randomness stream which can be useful for checking results during a run.
There's an argument for having global prng state in that the prng could
be preserved across power-loss, but I have yet to see a use for this,
and it would add a significant requirement to any future test/bench runner.
These are really just different flavors of test.py and test_runner.c
without support for power-loss testing, but with support for measuring
the cumulative number of bytes read, programmed, and erased.
Note that the existing define parameterization should work perfectly
fine for running benchmarks across various dimensions:
./scripts/bench.py \
runners/bench_runner \
bench_file_read \
-gnor \
-DSIZE='range(0,131072,1024)'
Also added a couple basic benchmarks as a starting point.
Christopher Haster