The lowercase -c/--compare felt clunky. I think because we tend towards
using uppercase for flags that operate on csv rows, such as -D/--define,
-L/--add-label (plot.py), etc.
This is useful for enforcing an upper-bound on fracs based on their
total component.
Technically possible via decomposing + min + recomposing, but... Well
which one do you think is easier?
- saturate(x)
- frac(min(max(int(x), 0), total(x)), total(x))
And this assumes x is easily available and not some other expr (though
chaining csv.py could work around that).
---
The motivation for this was `make bench-widths`, where one read
benchmark could ruin the entire column due to introducing infinities.
Now:
make bench # (squished a bit)
probe readed progged erased
b_wt_seq+w 1.0/1.0 (100.0%) 31.7/256.0 (12.4%) 4096.0/4096.0 (100.0%)
b_wt_random+w 1.0/1.0 (100.0%) 15.3/256.0 (6.0%) 4096.0/4096.0 (100.0%)
b_wt_logging+w 1.0/1.0 (100.0%) 15.4/256.0 (6.0%) 4096.0/4096.0 (100.0%)
b_wt_many+w 1.0/1.0 (100.0%) 16.1/256.0 (6.3%) 4096.0/4096.0 (100.0%)
b_rt_seq+r 1.0/1.0 (100.0%) 256.0/256.0 (100.0%) 4096.0/4096.0 (100.0%)
b_rt_random+r 1.0/1.0 (100.0%) 256.0/256.0 (100.0%) 4096.0/4096.0 (100.0%)
b_rt_many+r 1.0/1.0 (100.0%) 256.0/256.0 (100.0%) 4096.0/4096.0 (100.0%)
TOTAL 1.0/1.0 (100.0%) 149.0/256.0 (58.2%) 4096.0/4096.0 (100.0%)
# ^- notably not infinity
A simple float variant of the CsvFrac type:
- frac(1.5,2) => 1/2 (50.0%)
- ffrac(1.5,2) => 1.5/2.0 (75.0%)
Useful for `make bench-widths` (previously make bench-bus), where we
want to find the average buffer utilization:
probe readed progged erased
b_rbyd+create 1.0/1.0 (100.0%) 13.8/256.0 (5.4%) ∞/4096.0 (∞%)
b_rbyd+delete ∞/1.0 (∞%) ∞/256.0 (∞%) ∞/4096.0 (∞%)
b_rbyd+fetch 1.0/1.0 (100.0%) ∞/256.0 (∞%) ∞/4096.0 (∞%)
b_rbyd+lookup 1.0/1.0 (100.0%) ∞/256.0 (∞%) ∞/4096.0 (∞%)
b_rbyd+usage ∞/1.0 (∞%) ∞/256.0 (∞%) ∞/4096.0 (∞%)
b_wt_seq+w 1.0/1.0 (100.0%) 31.7/256.0 (12.4%) 4096.0/4096.0 (100.0%)
b_wt_random+w 1.0/1.0 (100.0%) 15.3/256.0 (6.0%) 4096.0/4096.0 (100.0%)
b_wt_logging+w 1.0/1.0 (100.0%) 15.4/256.0 (6.0%) 4096.0/4096.0 (100.0%)
b_wt_many+w 1.0/1.0 (100.0%) 16.1/256.0 (6.3%) 4096.0/4096.0 (100.0%)
TOTAL ∞/1.0 (∞%) ∞/256.0 (∞%) ∞/4096.0 (∞%)
Now that we have 4 types, the cast matrix gets a bit complicated, but
this is side-stepped a bit by a custom __frac__ hook.
---
Some other tweaks to csv.py:
- Added CsvFold.type to typecheck folds _after_ we know the expr's final
type.
- Adopted CsvFfrac as an output for most of the math functions/folds
- Stopped early termination of typechecking if we change type!
This was broken: int(float(1.5) + int(1))
This adds __hash__ to CsvFrac, and tweakes __eq__ to be more strict
about equality.
Previously CsvFrac only considered the relevant ratio for equality,
making hashing difficult:
- before: 1/2 == 2/4 => true
- after: 1/2 == 2/4 => false
But now that we have csv.py, with the explicit ratio function, it's
probably a good idea to be strict by default.
Note comparison is unchanged:
- 1/2 < 2/4 => false
- 1/2 > 2/3 => false
---
This popped up during debugging, and would be useful to have around.
Note CsvInt/CsvFloat already implicitly define __hash__ through
namedtuple's implicit __eq__ and friends. But this is disabled in
CsvFrac due to the explicit __eq__.
Which is good because otherwise it would've been wrong with the ratio
comparison!
--no-internal has already proven useful for skipping internal tests for
refactoring, so it makes sense to add --no-reentrant/fuzz flags as well.
--no-fuzz seems particularly useful for when you want to skip the less
targeted fuzz tests:
- with fuzz tests: 634616/634616 passed, in 1239.90s
- with --no-fuzz: 85434/85434 passed, in 423.41s
I also added runtime variants to test/bench_runner and test/bench.py.
These may be useful to skip tests without needing to recompile the
runner.
---
Also tweaked -s/--step to filter permutations in any --list-* flags, for
consistency.
This adds an explicit:
internal = true
As an alternative to:
in = 'lfs3.c'
For marking tests/benches as internal without actually placing them in a
specific source file.
The internal flag and --no-internal have proven suprisingly useful for
running a subset of tests when refactoring, as internal tests break much
more frequently than the high-level API. However, placing all the
internal tests in lfs3.c _has_ put a big strain on compilation/link
times.
`internal = true` now lets you mark tests/benches as internal, without
the extra compile/link overhead. You don't get access to any internal
things, but the flag can still be useful for filtering.
---
The original motivation for this was in the test_fwrite_clip_* tests,
but they ended up using lfs3_bptr_size to check leaf sizes, so oh well.
At least it's a good flag to have around. (In theory these could be made
"fake internal" with a manual bitmask, but it doesn't seem worth the
potential maintenance headache for saving a bit of link time. Though
maybe in the future priorities will change.)
Also cleaned up the handling of None in test/bench config a bit. Now
None should be equivalent to missing config fields, at the cost of more
noise in the Python code. None vs missing always feels unusually clunky
in Python.
Turns out mt.isinf is happy to accept non-primitive floats (such as
CsvFloat) as long as __float__ is defined. But CsvInt expects a float
inf, not a CsvFloat, so things explode later.
Fixed by explicitly casting to float if mt.isinf, instead of passing
as-is.
Also tweaked CsvInt/CsvFloat constructors to not bother checking
isinstance, unconditional int/float casts are probably cheaper than the
condition in Python.
This mirrors test_runtime in test.py, which has been useful for finding
test cases that are slowing down our tests.
Though note bench.py's output is per-probe, so summing bench_runtime
would be longer than the total runtime of the bench if multiple probes
are involved. Probes can be nested, so I'm not sure this is avoidable. I
guess it's the worst-case runtime if all probes were run independently?
Also note, confusingly, bench_runtime is cumulative while bench_simtime
remains per-sample. Maybe this will help prevent interchanging the two?
This is the inverse of accumulate, returning the difference between
subsequent results. In theory accumulate(delta(x)) and
delta(accumulate(x)) are noops.
This is particularly useful for normalizing our bench n value in
scripts. It's the only value still returned as a cumulative measurement,
which is a bit inconsistent, but necessary for uniquely identifying
probe steps.
Note this matches the behavior of mods, e.g. I would expect this to not
break if ORDER is missing:
./scripts/csv.py \
-bcase='%(case)s+%(probe)s+%(ORDER)s' \
-ft=accumulate(bench_simtime, case, probe, ORDER)
Normally the expr compiler would force typechecking of ORDER, giving it
a default value of int(0) if missing, but we intentionally bypass
typechecking in enumerate/accumulate's by fields since they may be
strings.
I think this is currently only possible with overlapping by/field
fields, but hiding results with conflicting by fields is not ideal.
Especially since this function is central to so many scripts:
cat test.csv
a,b,c
x,2,1
x,1,2
x,1,3
Before:
./scripts/csv.py test.csv -ba -bb -fb -fc
warning: by fields are unstable
a,b b c
x,2 2 1
TOTAL 4 6
After:
./scripts/csv.py test.csv -ba -bb -fb -fc
a,b b c
x,2 2 5
x,2 2 1
TOTAL 4 6
This solves the main issue with unstable by fields, so no more warning.
Note that some features rely on by being unique to work (added/removed
numbers, compare fields, etc). They shouldn't error, but may be
incorrect/unintuitive with conflicting by fields, so avoiding
conflicting by fields is still a good idea.
So it turns out this _can_ happen, without an in-script coding error.
Consider the behavior of a script with overlapping by/field fields:
$ cat test.csv
a,b
x,2
x,1
x,1
$ ./scripts/csv.py test.csv -ba -bb -fb
During the first fold, rows 2 and 3 will contain b=1, but during the
second fold they will have been merged, resulting in b=2.
So, relaxing to a warning for now. Maybe the table renderer should be
rewritten to avoid folding? (note diffing results may be tricky)
The main changes:
- Added TEST_DEFINES and BENCH_DEFINES to allow overriding the default
test/bench define header:
-DTEST_DEFINES=my_test_defines.h
Note these are VERY different from LFS_DEFINES upstream. They aren't a
typical header file, and are included multiple times with various
query macros.
It's hacky, but works surprisingly well.
Or maybe I'll just do anything to avoid having to write multiline
macros. Ugh, backslashes.
- Moved more logic into bench/test_defines.h, including everything
needed to integrate other filesystems out-of-tree.
This mostly meant moving all of the cfg initialization logic into its
own query macro (replacing the BENCH/TEST_CFG field macros).
But this also includes a bunch of small tweaks encountered while trying
to get external benchmarks running again.
The external benchmarks include several other filesystems (littlefs2,
SPIFFS, Yaffs2), and I'm hoping this injectable/queryable header thing
will do a good job at avoiding a maintenance headache. (At least a
better job than forking bench_runner.c, which was the previous
solution.)
Now -l/--list-fields includes however many results fit in 36 chars:
$ ./scripts/csv.py --list-fields test.csv
i int # 16,17,14,18,19,15,20,13,12,29,27,28,...
suite ? # bench_p26_wt
case ? # bench_p26_wt_linear,bench_p26_wt_ran...
NO_FRUNCATE int # 0
SIZE int # 2097152
SEED int # 42
The whole point of -l/--list-fields is to give a quick information dump
about what's inside a csv file, and we're already parsing everything to
try to figure out types, so why not?
Much easier to read than head:
$ head -n5 test.csv
i,suite,case,NO_FRUNCATE,SIZE,SEED,BLOCK_SIZE,FILE_SIZE,SIM_...
16,bench_p26_wt,bench_p26_wt_linear,0,2097152,42,65536,64,36...
16,bench_p26_wt,bench_p26_wt_linear,0,2097152,42,65536,64,36...
16,bench_p26_wt,bench_p26_wt_linear,0,2097152,42,65536,64,36...
16,bench_p26_wt,bench_p26_wt_linear,0,2097152,42,65536,64,36...
This extends csv.py's enumerate/accumulate exprs with optional by field
arguments. Each set of by fields gets its own state, allowing multiple
parallel enumerates/accumulates to be processed simultaneously.
This is especially useful when the number of by field sets is unknown.
In theory you could split/merge each by field set with a separate csv.py
call, but it'd be a real pain.
Consider some bench results:
case,n,simtime
bench_rbyd,1,100
bench_rbyd,2,10
bench_rbyd,3,100
bench_btree,1,200
bench_rbyd,4,10
bench_btree,2,20
bench_btree,3,2000
bench_btree,4,200
It was a bit awkward to handle these with csv.py's accumulate, as
accumulate operated strictly per-row, ignoring the case field.
But now with optional by fields:
$ ./scripts/csv.py test.csv \
-bcase -bn \
-fsimtime='accumulate(simtime, case)'
case,n simtime
bench_btree,1 200
bench_btree,2 220
bench_btree,3 2220
bench_btree,4 2420
bench_rbyd,1 100
bench_rbyd,2 110
bench_rbyd,3 210
bench_rbyd,4 220
TOTAL 5700
Note that these by fields are a bit special in csv.py's grammar. So far,
they are the only fields in field exprs that aren't typechecked. The
alternative would be string types in csv.py, but I'm not sure I want to
go that far.
---
It's tempting to try to invert this logic (accumulate(simtime, n)), but
I'm not sure how it would work internally. The duplicate by fields
("case") do get annoying, but specifying them in the expr helps make the
relevant state explicit.
Keep in mind we don't evaluate the actual by fields until much later in
csv.py. Entangling these stages risks confusion (-ba='%(b)s'
-c='enumerate(n)'? hidden by fields? overlapping by+field fields?).
I mean, what would you expect this to do?
max(a) + sum(b)
Whatever your answer is, it's wrong (the way csv.py works, we always
compute folds after expr evaluation). The best option is to error,
matching the behavior of mismatched types.
csv.py's -L/--list-computed was returning some confusing types:
$ ./scripts/csv.py /dev/null -fa='float(1)' -L
a int sum
^-- huh!?
Turns out csv.py's fold typechecking was all broken. Folds can change
the type, but only at the invocation:
$ ./scripts/csv.py /dev/null -fa='sum(float(1))' -L
a int sum
$ ./scripts/csv.py /dev/null -fa='avg(int(1))' -L
a float avg
$ ./scripts/csv.py /dev/null -fa='int(avg(1))' -L
a float avg
This is maybe defensible for explicit folds, since their evaluation is
also lifted, but not so much for things like literals/fields/etc.
---
Fixed by allowing None to indicate a generic fold, and allowing types to
be lazily figured out in csv.compile.
By "simple" I mean any non-globbing suite/case ids.
Non-globbing suite/case ids can be filtered early in the test_runner.
But globbing ids require, surprise, globbing, which is currently handled
by test/bench.py.
---
This greatly speeds up valgrind testing of specific suites/cases,
otherwise things get bogged down during the initial --list-cases due to
the sheer number of test permutations we've accumulated.
Maybe we shouldn't be running the initial --list-cases under Valgrind,
but oh well. This mostly solves the problem without too many changes.
This needed a different name, and "bench probe" is sort of reminiscent
of the "debug probes" you can use to measure things in the real world.
Maybe this is just my embedded engineering background poking through,
but honestly anything is better than a single char m, especially for a
non-integer field.
These seem useful enough to have shortform flags:
- -l/--list-fields - Input fields before processing
- -L/--list-computed - Computed fields and expr dependencies
Note while -L/--list-computed has more information, it's also more
likely to trigger an assert/error due to poorly implemented field exprs.
On one hand, only inferring the used input fields is conceptually
correct because that's how csv.py works. On the other, it doesn't really
make sense for --list-computed to show _less_ information than
--list-fields.
So, showing all inferred types now:
$ ./scripts/csv.py --list-computed test.csv \
-bcase='%(case)s+%(m)s' \
-fsimtime='float(bench_simtime)/1.0e9' \
-fsimthroughput='float(n)/max(float(bench_simtime)/1.0e9,1.0e-9)'
i int .--> case ? ?
suite ? |.-> simtime int sum
case ? -+|.> simthroughput int sum
SKIP_WARMUP int |||
FILE_SIZE int |||
SEED int |||
...
m ? -'||
n int ---+
bench_reads int ||
bench_progs int ||
bench_erases int ||
bench_readed int ||
bench_progged int ||
bench_erased int ||
bench_simtime int ---'
I think this makes --list-computed a strict superset of --list-fields
now.
I was expecting -ba -Fa to sort numerically, but it was not. Turns out
hidden field fields (-F/--hidden-field) without exprs were never
typechecked.
This is not an issue for non-hidden field fields (-f/--field), because
we typecheck these explicitly in compile.
Found from some confusing behavior when by/from fields overlap. It turns
out when this happens (-bhi -Fhi, for example), the generated getattr
for the by field would trigger the __getattribute__ for the overlapping
field field, resulting in a fold on _every add operation_.
Hopefully you can see where this is a bit of a problem when summing a
large number of results (O(n^2)?).
---
Fixed by switching getattr to object.__getattribute__ and reconsidering
csv.py's entire design.
Now that we have csv.py's accumulate(), this information is strictly
redundant!
$ ./scripts/csv.py test.csv \
-bspecific_permutation_here \
-fbench_creaded='accumulate(bench_readed)'
The point of adding accumulate() was to drop these. We really shouldn't
be doubling the size of the csvs with redundant/derivable data.
Less useful than --list-fields, but fun.
This shows more of the internal expr eval info: input fields + types,
output fields + types + folds, and a small dependency graph showing what
goes where:
$ ./scripts/csv.py --list-computed test.csv \
-bcase='%(case)s+%(m)s' \
-fsimtime='float(bench_simtime)/1.0e9' \
-fsimthroughput='float(n)/max(float(bench_simtime)/1.0e9,1.0e-9)'
i ? .--> case ? ?
suite ? |.-> simtime int sum
case ? -+|.> simthroughput int sum
SKIP_WARMUP ? |||
FILE_SIZE ? |||
SEED ? |||
...
m ? -'||
n int ---+
bench_reads ? ||
bench_progs ? ||
bench_erases ? ||
bench_readed ? ||
bench_progged ? ||
bench_erased ? ||
bench_simtime int ---'
Maybe I was just itching to write another ascii-art renderer.
One issue I keep running into with csv.py is that it's difficult to get
started with a new/unfamiliar csv file.
csv.py itself doesn't know what to do until you start specifying fields,
but you can't start specifying fields until you know what fields there
are. Add to this the fact that our csv files have so much info shoved in
them that their "human readability" is mostly theoretical.
The --list-fields flag provides a quick solution to this:
$ ./scripts/csv.py --list-fields test.csv
i int
suite ?
case ?
SKIP_WARMUP int
FILE_SIZE int
SEED int
...
csv.py doesn't have much info at this stage, but we can at least include
the best-effort type guessing we use for field exprs.
Now that we have the enumerate expr, -i/--enumerate can be implemented
entirely during expr eval:
- -i/--enumerate => -bi -Fi=enumerate()
- -I/--hidden-enumerate => -Bi -Fi=enumerate()
Instead of internally reimplementing the same behavior.
This is what our help text implies, so might as well put our money where
our mouth is. And the less special internals we have, the better.
I considered removing -i/-I completely, but it's quite a convenient flag
when debugging csv.py expressions.
In an effort to move away from magic usage of -i/--enumerate, this adds
an explicit z field for differentiating -r/--hot results (and for normal
recursive results).
Instead of trying to think of a new flag to control this, this just
piggybacks on -Z/--children, which now accepts a tuple:
- ./scripts/csv.py -z3 -Z
- ./scripts/csv.py -z3 -Zchildren
- ./scripts/csv.py -z3 -Zz,children
The only tricky bit was needing to insert z in front of the by fields,
otherwise it was mostly a simplification from the enumerate mess.
Another positive side-effect: -r/--hot (and -z/--depth) now implies
-Zz,children, removing the annoying/confusing behavior of hotify folding
results by default.
The current... attempt at an approach was broken and becoming horribly
unmaintainable. Two issues found without even looking:
1. Field inference didn't understand prefixes, leading to duplicate
by/field fields when attempting to infer by fields with --prefix.
2. Sort wasn't working for some reason, probably because they behavior
of sort, defines, etc are really weird since they apply to both by
fields and field fields.
I considered just dropping support for --prefix completely, this really
isn't worth the time, but instead found a simple solution of moving
prefix handling to one of the first steps in collect_csv.
This has the downside of creating conflicts when a prefixed/non-prefixed
field has the same name, but I don't care. --prefix is a niche flag that
shouldn't mess with the rest of the code like this, and none of the
other scripts really handle field conflicts correctly anyways.
- Fixed the initial filter using explicit 'children'/'notes' literals
Whoops, how did this happen?
- Fixed fold using default children/notes result attributes
This one is a bit more excusable, self.children is easy to overlook.
But not actual string literals, that's silly.
This adds two new exprs to csv.py, useful for sequential data:
enumerate() A number incremented each result
accumulate(a) A running sum across results
To make these work required adding support for cross-row state, thus the
new state field in CsvExpr.Expr.eval.
Once you have that cross-row state, implementing enumerate/accumulate is
pretty straightforward. The only complication being that we need to hash
state by the unique Python id (`id(self)`), otherwise multiple exprs
would share state, which would be pretty weird.
Note that csv.py's pipeline is now quite complex, and stage order is
important!
input --> define --> expr --> folding --> sorting --> output
filtering eval
As a result, it's unfortunately not possible to organize enumerate/
accumulate by by fields. I poked around with the idea but decided it was
too complex (aren't I supposed be building a filesystem?). The guiding
principle behind csv.py is most problems can be solved with more process
substitution.
---
This is a bit clunky since we can't use the existing fold system, but
csv.py is already a pile of hacks, so what's one more?
The reason for the clunkiness is that the original idea behind csv.py
was to treat each folded row independently and order-agnostic. Not the
greatest idea in hindsight, cross-row operations are useful!
The idea here is to add some sort of accumulate operation to csv.py, so
we can stop cumulative-result clunkiness. It would also be immensely
useful as a general function, and -i/--enumerate already sets a
precedent for this sort of cross-row behavior.
But I'm starting to think using flags here is not the best way, maybe
this would be better as a field expr?
For some reason -F/--hidden-field fields weren't being parsed as a
CsvExpr, breaking any attempt to use exprs with hidden fields. Probably
just broken during a refactor.
Fortunately an easy fix.
The value of simtime isn't actually the simtime value, but the
simulated throughput, which is easy enough for our csv.py script to
calculate (with a daintily placed max to avoid divide-by-zero).
Throughput has the benefit of being somewhat size-agnostic, making
cross-benchmark comparisons easier.
I guess it's technically possible to do something similar with
readed/progged/erased numbers, but conceptually that would be really
confusing...
---
Also renamed test/bench_time -> test/bench_runtime to hopefully prevent
confusion between the two time spaces.
This is based on some work in external benchmarks. What's worked well
there is emulating a global simtime based on per-byte estimates.
This moves the emulated simtime into emubd/kiwibd, and extends the idea
with both per-byte and per-op timing estimates for hopefully more
realistic results.
---
The problem is how NAND flash reads work.
Per-byte timing estimates are surprisingly accurate for NOR flash. There
is some overhead for sending the address, but it's mostly dominated by
bus cost (~20ns/B [1]).
NAND flash, on the otherhand, technically does support byte-level reads,
but first needs to read into 2KiB buffer. Surprisingly, these are pretty
close in cost (~19ns/B bus [2] vs ~12ns/B buffer [2]).
This close-ness makes modeling NAND flash difficult. If we set
read_size=1, we risk hiding the cost of small reads, which littlefs3 is
full of (rbyd lookups). If we set read_size=2048, we unfairly penalize
littlefs3 for the same reason.
---
The solution here is to expose both per-byte and per-op timing
estimates. This lets you model NAND reads using two data points:
^
| realtime --> ...............o
| : .....'''' :
| ...............:'''' ^ :
| :....''''' | :
| ..........:::::: simtime :
| .....:'''' :
|o....:::::.....: :
|: :
|: :
+:-----------------------------------------------------------:>
min read max read
Where:
bus_timing = 19ns
buffer_timing = 25us
buffer_size = 2KiB
erase_size = 128KiB
min_read = buffer_timing
max_read = (erase_size/buffer_size)*buffer_timing - buffer_timing
read_timing = min_read
readed_timing = ((max_read - min_read)/erase_size) + bus_timing
simtime = reads*read_timing + readed*readed_timing
(per-op) (per-byte)
This should correctly penalize small reads without complicating
emubd/kiwibd too much.
That's the idea anyways! It will take some use to understand if this is
a reasonable approach.
As a plus, this is a superset of the per-byte model, so both can be used
for realistic vs idealistic simulations (and to test the bus+buffer
model itself).
1: https://www.winbond.com/resource-files/W25Q256JV%20SPI%20RevQ%2002072025%20Plus.pdf
2: https://www.winbond.com/resource-files/W25N01GV%20Rev%20R%20070323.pdf
- Delayed defines/permutations assignment until after generation. Just a
bit of code smell.
- Expanded all __eq__, __ne__, __lt__, __gt__, etc magic methods, just
to minimize surprises in the future.
This extends our ifdef/ifndef test attributes to support more
complicated logic expressions.
So far we haven't really needed this (ifdef/ifndef accepts an implicitly
anded list, which has covered everything so far), but I realized there's
a simple trick to make this work.
For example, in test.toml:
ifdef = 'A && !(B || C)'
Generated ifdef:
#if (defined(A) && !(defined(B) || defined(C)))
This doesn't require complex parsing or anything, just a simple regex:
s/[a-zA-Z_0-9]\+/defined(&)/g
Is using #if defined(A) everywhere instead of #ifdef A more expensive
for the compiler? Not sure. But it seems like we're heavily dominated by
the single-threaded link time, so I'm not sure we care.
This started with adding -d/--diff support to dbgflags.py, which is very
useful for comparing flags during test failure.
The flag asserts in our tests generally look like this:
tests/test_mount.toml:171:assert: assert failed with 33570064,
expected eq 33570576
assert(fsinfo.flags == (
Which can now be quickly compared with dbgflags.py:
$ ./scripts/dbgflags.py +i 33570064 -d 33570576
LFS3_I_GBMAP 0x02000000 Global on-disk block-map in use
LFS3_I_REVPERTURB 0x00000010 Mounted with LFS3_M_REVPERTURB
LFS3_I_MKCONSISTENT 0x00000100 Filesystem needs mkconsistent to write
-LFS3_I_LOOKAHEAD 0x00000200 Lookahead buffer is not full
LFS3_I_PREERASE 0x00000400 Blocks can be pre-erased
LFS3_I_COMPACT 0x00000800 Filesystem may have uncompacted metadata
LFS3_I_CKMETA 0x00001000 Metadata checksums not checked recently
LFS3_I_CKDATA 0x00002000 Data checksums not checked recently
The assert print is a bit more annoying than it needs to be, as it only
prints in decimal. But, since our prettyasserts.py only works at the
syntax layer, it's not possible to make it any smarter.
---
To make this diffing work required a couple more features in our
self-parsing Flag class:
- Keep track of lineno, mainly for ordering things
- Moved find logic into a staticmethod on all classes
- Added _sentinel based defaults to find functions
- Allowed self to be non-class in line functions to deduplicate "Unknown
flag" messages
I went ahead and extended these to the other self-parsing classes (Err
and Tag) in case they're useful in the future.
The main change is adding LFS3_M_REVPERTURB, which will be necessary for
preerase allocations, but I got distracted and ended up giving the
revision count subsystem a bit of a refactor.
Main changes:
- Added LFS3_M_REVPERTURB, which ensures the leading bit in the
revision count changes after each allocation/relocation/compaction.
This is generally optional, but will be required for preerase
allocations. Our ecksum system is only reliable if we ensure at least
one bit changes, otherwise the chance of ecksum collision is very
high.
The downside of LFS3_M_REVPERTURB is that we need to read the contents
of the new block to figure out what the bit should change to. Probably
a minimal cost in the system, but still a good reason to make the
behavior optional.
Does LFS3_M_REVPERTURB have any use outside of preerased allocation?
I'm not sure. Maybe it has some niche use reducing the chance of bd
ECC collisions?
- Dropped LFS3_M_REVDBG, but adding low-effort debug bits that are
always enabled.
Making LFS3_M_REVDBG conditional was probably overkill. The flag
checks probably cost more than the actual debug bits when enabled.
Instead, replaced with a simpler, low-effort debug bit system, where
we only set the debug bits during mdir allocation/relocation. These
bits shouldn't change during normal compaction, but we _don't_
introduce debug bits if mounting a filesystem from a driver without
these debug bits.
- Restricted recycle counter to at most 20-bits to make space for
things. This ensures perturb/debug bits don't get overwritten (though
we really only care about perturb bits).
2^20 (~1M) recycles is probably enough for any device littlefs will
run on, especially considering the recycle_count should probably be
several orders of magnitude smaller than the device's expected erase
cycles.
Worst case this can always be increased in the future without
backwards incompatible changes. The only hard requirement for revision
counts is that the full 32-bits are comparable.
- Simplified lfs3_rev_inc and friends, and moved most of the
disk-dependent revision count stuff down into lfs3_rbyd appendrev.
This deduplicates the messy revision count handling in
lfs3_btree_commit_.
Though note the implicit lfs3_rbyd_appendrev now defaults to writing
the btree debug bits ('b'). A bit of a hack, but works for littlefs.
Here's the resulting encoding:
vvvv---- -------- -------- -ddddddd
vvvvrrrr rrrrrr-- -------- -ddddddd
vvvvrrrr rrrrrrnn nnnnnnnn pddddddd
'-.''----.----''----.----' ^'--.--'
'------|----------|------|---|---- 4-bit relocation revision
'----------|------|---|---- recycle-bits recycle counter
'------|---|---- pseudorandom noise (if revnoise)
'---|---- perturb bit (if revperturb)
'---- low-effort debug bits
11-1--- - h = mroot anchor
11-11-1 - m = mdir
11---1- - b = btree node
Note we store revision counts as le32s, so the perturb bit should end up
as the leading bit in the first byte.
Costs a bit more code (mostly because the debug bits are now
unconditional, even if low-effort), but simplifies the codebase:
code stack ctx
before: 35124 2136 660
after: 35144 (+0.1%) 2136 (+0.0%) 660 (+0.0%)
after+yesrevperturb: 35192 (+0.2%) 2136 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap+np before: 38252 2144 776
gbmap+np after: 38272 (+0.1%) 2144 (+0.0%) 776 (+0.0%)
gbmap+np after+yrp: 38328 (+0.2%) 2144 (+0.0%) 776 (+0.0%)
code stack ctx
gbmap+yp before: 38832 2168 796
gbmap+yp after: 38852 (+0.1%) 2168 (+0.0%) 796 (+0.0%)
gbmap+yp after+yrp: 38908 (+0.2%) 2168 (+0.0%) 796 (+0.0%)
Allocating pre-erased blocks gets quite complicated due to our
restricted flash model, but at least the actual pre-erasing is
relatively straightforward:
- We keep track of known preerased state in lfs3->gbmap.preeraser.
- If LFS3_GC_PREERASE is provided during gc work, we increment the
preeraser's known window by scanning the gbmap.
- Any BMFREE ranges we find, we erase a block at a time, and store the
resulting ecksum in a BMERASED range in the gbmap.
- We keep track of how many blocks we erased, and stop early if this
exceeds cfg.gc_preerase_count. This just lets users tune how many
blocks to preerase in case something (?) prevents preerased blocks
from being used.
Some notes:
- We don't really do anything with ranges in lfs3_alloc_preerase. In
theory we could bulk in erase to minimize the number of commits to the
gbmap, but we expect erase to dominate, so this probably isn't worth
it.
And if erase doesn't dominate, why would you bother pre-erasing
blocks?
- Preerasing isn't really a traversal operation, and is managed by a
sort of secondary state machine in lfs3_fs_gc_.
This also means lfs3_trv_read with LFS3_T_PREERASE does nothing, but I
guess that is ok? It's tempting to try to make lfs3_trv_read also
preerase, but it's unclear what block it should return -- it's
probably the wrong API.
- Introducing ecksums actually went quite a bit smoother than I
expected. Though it helps ecksums are the only optional payload, no
type punning or anything.
Ecksums do muddy the gbmap's design a bit, unfortunately. The main
issue being that we can only merge BMERASED ranges with equal ecksums.
This makes BMERASED ranges less compressable than the others, and may
be one reason to limit cfg.gc_preerase_count.
However:
1. This is where I think it's useful to emphasize that the gbmap's
responsibility is to track _free_ blocks, in-use blocks are
secondary.
When allocating, we're going to stop at the first BMFREE/BMERASED,
but may need to skip over an unbounded number of BMINUSE/BMBAD
blocks. So the compressability of BMFREE/BMERASED ranges should
have less of an impact on block allocation.
2. In practice, most flash uses consistent erase values, so the
resulting ecksums will probably be compressable. The exceptions are
noop-erases (SD/eMMC, RAM, NVRAM, etc), and encryption with block
address permutation?
Though noop-erases are a pretty big exception.
Code changes:
code stack ctx
before: 35116 2136 660
after: 35116 (+0.0%) 2136 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap+np before: 38040 2136 776
gbmap+np after: 38188 (+0.4%) 2144 (+0.4%) 776 (+0.0%)
code stack ctx
gbmap+yp before: 38040 2136 776
gbmap+yp after: 38608 (+1.5%) 2144 (+0.4%) 796 (+2.6%)
Also tweaked related flag comments a bit.
---
This adds another internal flag modifier ('a') to dbgflags.py to
indicate a flag is an alias for multiple other flags.
These still show up in -l/--list and name searches:
$ ./scripts/dbgflags.py -l +ck
LFS3_CK_MKCONSISTENT 0x00000100 Make the filesystem consistent
LFS3_CK_LOOKAHEAD 0x00000200 Repopulate lookahead buffer
LFS3_CK_COMPACT 0x00000800 Compact metadata logs
LFS3_CK_CKMETA 0x00001000 Check metadata checksums
LFS3_CK_CKDATA 0x00002000 Check metadata + data checksums
LFS3_CK_CK 0x00003000 Alias for all check work
LFS3_CK_GC 0x00003b00 Alias for all gc work
But are hidden from value searches, as they would be redundant and the
specific low-level flags are probably more useful:
$ ./scripts/dbgflags.py +ck 0x00003000
LFS3_CK_CKMETA 0x00001000 Check metadata checksums
LFS3_CK_CKDATA 0x00002000 Check metadata + data checksums
This effectively reverts 1f824a0:
- LFS3_T_COMPACTMETA -> LFS3_T_COMPACT
- gc_compactmeta_thresh -> gc_compact_thresh
And friends.
After using LFS3_T_COMPACTMETA for a bit, I think it just adds noise
without much value. Especially when next to LFS3_T_LOOKAHEAD,
LFS3_GC_PREERASE, LFS3_M_SYNC, etc.
It's interesting that we already have some very distinct verbs for this
sort of thing based on data type (compact => metadata, garbage-collect
=> disk, compress => data).
dbgflags.py now uses +flags to indicate flag namespaces, but our gdb
script only forwarded -f/--flags, which made dbgflags a bit of a pain
to use in the debugger!
Fortunately an easy fix.
Now this works:
(gdb) dbgflags +t trv.gc.t.h.flags
LFS3_T_RDWR 0x00000000 Open traversal as read and write
LFS3_T_MKCONSISTENT 0x00000100 Make the filesystem consistent
LFS3_T_LOOKAHEAD 0x00000200 Repopulate lookahead buffer
LFS3_t_TRAVERSAL 0x60000000 Type = traversal
LFS3_t_MDIR 0x00010000 Btype = mdir
Our flag space is already really packed, and I'm not sure having these
as separate flags is meaningful or useful for users. They both indicate
to repopulate allocators, and most users probably won't care that there
are two subtly different allocators operating under the hood.
There's an argument that LOOKAHEAD not touching disk is a useful
distinction, but in practice you really only need LOOKAHEAD work when
mounted RDWR.
So, merged the behaviors of LOOKAHEAD + LOOKGBMAP such that
LFS3_*_LOOKAHEAD requests repopulation of all allocators based on
gc_lookahead_thresh and gc_lookgbmap_thresh.
In priority order (some notes below):
1. If max(lookahead, gbmap) < gc_lookahead_thresh => repop lookahead
2. If gbmap < gc_lookgbmap_thresh => repop gbmap
As a plus, this makes it easier to avoid LFS3_IFDEF_GBMAP mess.
---
It's interesting to note LFS3_*_LOOKAHEAD will still repopulate the
lookahead buffer when the gbmap is present, but only if this would gain
more knowledge than was is currently in the gbmap.
I considered disabling lookahead scans completely when we have a gbmap,
but repopulating the lookahead buffer is still useful if the gbmap is at
risk of exhaustion. This is what gc_lookahead_thresh is for anyways, and
users can set gc_lookahead_thresh=0 if they want to disable this
behavior.
Relatedly, lookahead scans are actually prioritized over gbmap scans
(when they would gain knowledge). In theory this minimizes gc latency,
as gbmap scans risk triggering a full lookahead scan when building the
new gbmap.
---
Code changes minimal:
code stack ctx
before: 35152 2136 660
after: 35152 (+0.0%) 2136 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap before: 38076 2136 776
gbmap after: 38080 (+0.0%) 2136 (+0.0%) 776 (+0.0%)
The idea is this is similar to ~ for the home directory, hopefully
simplifying littlefs path parsing in scripts:
- /hi -> hi in root dir
- ./hi -> hi in current dir
- ../hi -> hi in parent dir
- ~/hi -> hi in home dir
- %/hi -> hi in littlefs root dir
Note this only works when standalone:
- ~hi != ~/hi
- %hi != %/hi
And files named % can still be referenced with a ./ prefix:
- ./% -> % in current dir
- %/% -> % in littlefs root dir
---
This is probably overkill for dbglfs3.py, as the arg ordering was
already enough to disambiguate disk path vs mroot address vs littlefs
path, but eventually I think the idea will be useful for more powerful
scripts.
A hypothetical:
$ mklfs3 cp disk -b4096 -r image_files %/image_files
This is still a hack to make the seek _enum_ appear somewhat readable in
our dbg _flags_ script. But the previously internal SEEK_MODE was
causing all seek flags to be hidden from -l/--list confusingly.
Christopher Haster