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Fixed unaligned data checksumming in two ways (uncrc32c, flcksum)

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Checksumming unaligned data during block compaction is surprisingly
tricky. We don't know if our data will be aligned until after
a potentially unbounded number lookups, we need to write data into our
pcache as we go to avoid unnecessary lookups, but if we end up unaligned
we need to revert our checksum to the checksum of the aligned data.

The way I see it there are 4 options:

1. Calculate the checksum after writing data into the block.

   This is the most expensive option, requiring a full second read of
   the data to calculate the checksum. It is simple though.

2. Do a pass over the btree to figure out alignment before writing.

   This at least only reads metadata twice, so is more efficient than
   the 1st option.

3. Keep track of the aligned checksum on each flush, falling back to the
   last flushed checksum if we need to correct alignment.

   This solution is flexible though requires some extra state to track
   multiple checksums.

4. Leverage the math behind CRCs to run the CRC backwards when we
   truncate for alignment.

   This works, though a bit inefficiently, but is strictly tied to
   CRC-related checksums.

   By inefficient I mean that we would likely be limited to a bit-level
   "uncrc32c". It's possible to create nibble/byte tables for uncrc32c,
   but this adds significant code cost for a relatively uncritical
   function.

   I was hopeful that we could leverage the existing tables in both
   functions, but unfortunately it doesn't work out like that. You could
   scan the crc32c table to find the constant to reverse, but this
   requires ~16*2 or ~256 operations vs "naive" ~8 operations per byte.

This commit implements both 3 and 4, defaulting to 4 unless
LFS_NO_UNCRC32C is defined.

The current lfs_uncrc32c implementation is a simple bit-level
implementation, but does allow for crc32c truncation without any extra
state.

              code          stack
  before:    32044           2880
  uncrc32c:  32108 (+0.2%)   2880 (+0.0%)
  flcksum:   32132 (+0.3%)   2880 (+0.0%)
This commit is contained in:
Christopher Haster
2023-12-15 00:58:24 -06:00
parent c2e3a391ff
commit 006d656da2
4 changed files with 208 additions and 86 deletions
Download Patch File Download Diff File Expand all files Collapse all files
tests/test_rbyd.toml
+108 -54
View File
@@ -2495,8 +2495,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// update each tag in permutation order
for (unsigned j = 0; j < N; j++) {
@@ -2783,8 +2785,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(-1, RM(UATTR(j+1)), 0, NULL())))
@@ -2928,8 +2932,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(-1, RM(UATTR(j+1)), 0, NULL()))) => 0;
@@ -3494,8 +3500,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// remove each tag in permutation order
for (unsigned j = 0; j < N; j++) {
@@ -5978,8 +5986,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// update each tag in permutation order
for (unsigned j = 0; j < N*M; j++) {
@@ -6121,8 +6131,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j/M, RM(UATTR((j%M)+1)), 0, NULL()))) => 0;
@@ -6301,8 +6313,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// remove each tag in permutation order
for (unsigned j = 0; j < N*M; j++) {
@@ -7189,8 +7203,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j, RM, -1, NULL()))) => 0;
@@ -7349,8 +7365,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j, RM, -1, NULL()))) => 0;
@@ -7532,8 +7550,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j, RM, -1, NULL()))) => 0;
@@ -7662,8 +7682,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j, RM, -1, NULL()))) => 0;
@@ -8030,8 +8052,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// delete each rid in permutation order
for (unsigned j = 0; j < N; j++) {
@@ -8178,8 +8202,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// delete each rid in permutation order
for (unsigned j = 0; j < N; j++) {
@@ -10128,8 +10154,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j*W+W-1, RM, +D, NULL()))) => 0;
@@ -10255,8 +10283,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j*W+W-1, GROW(REG), +D,
@@ -10391,8 +10421,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j*W+W-1, GROW(UATTR(1)), +D,
@@ -10539,8 +10571,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j*W+W-1, GROW, -D, NULL()))) => 0;
@@ -10666,8 +10700,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j*W+W-1, GROW(REG), -D,
@@ -10802,8 +10838,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j*W+W-1, GROW(UATTR(1)), -D,
@@ -10949,8 +10987,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j*W+W-1, RM, -W, NULL()))) => 0;
@@ -11104,8 +11144,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
LFSR_ATTR(j*W+W-1, UATTR(1), 0,
@@ -11712,8 +11754,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// remove with a wide tag
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
@@ -11849,8 +11893,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// replace with bitwise inverse
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
@@ -12079,8 +12125,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// remove with a wide tag
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
@@ -12225,8 +12273,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// replace with bitwise inverse
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
@@ -12456,8 +12506,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// remove with a wide tag
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(
@@ -12595,8 +12647,10 @@ code = '''
rbyd = backup_rbyd;
lfs_bd_erase(&lfs, rbyd.blocks[0]) => 0;
lfs_bd_prog(&lfs, &lfs.pcache, &lfs.rcache, false,
rbyd.blocks[0], 0, backup_block, rbyd.eoff) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false) => 0;
rbyd.blocks[0], 0, backup_block, rbyd.eoff,
NULL) => 0;
lfs_bd_flush(&lfs, &lfs.pcache, &lfs.rcache, false,
NULL) => 0;
// replace with bitwise inverse
lfsr_rbyd_commit(&lfs, &rbyd, LFSR_ATTRS(