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runners: emubd/kiwibd: Adopted emulated simtime API

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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
This commit is contained in:
Christopher Haster
2026-01-18 23:57:23 -06:00
parent 1b70c1f199
commit d3dd927de3
10 changed files with 548 additions and 278 deletions
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tests/test_ck.toml
+24 -24
View File
@@ -1493,7 +1493,7 @@ code = '''
(lfs3_size_t)BADBLOCK, badbit/8, badbit, badbit/8, badbit%8);
// mark our badbit as bad
lfs3_emubd_markbadbit(CFG, BADBLOCK, badbit) => 0;
lfs3_emubd_mkbadbit(CFG, BADBLOCK, badbit) => 0;
// formatting the filesystem may already find the bit error
lfs3_t lfs3;
@@ -1552,7 +1552,7 @@ code = '''
corrupt:;
// reset badbit
lfs3_emubd_markgood(CFG, BADBLOCK) => 0;
lfs3_emubd_mkgood(CFG, BADBLOCK) => 0;
}
'''
@@ -1610,7 +1610,7 @@ code = '''
badblock, badbit/8, badbit, badbit/8, badbit%8);
// mark our badbit as bad
lfs3_emubd_markbadbit(CFG, badblock, badbit) => 0;
lfs3_emubd_mkbadbit(CFG, badblock, badbit) => 0;
// format
lfs3_t lfs3;
@@ -1660,7 +1660,7 @@ code = '''
lfs3_unmount(&lfs3) => 0;
// reset badbit
lfs3_emubd_markgood(CFG, badblock) => 0;
lfs3_emubd_mkgood(CFG, badblock) => 0;
}
'''
@@ -1721,7 +1721,7 @@ code = '''
badblock, badbit/8, badbit, badbit/8, badbit%8);
// mark our badbit as bad
lfs3_emubd_markbadbit(CFG, badblock, badbit) => 0;
lfs3_emubd_mkbadbit(CFG, badblock, badbit) => 0;
// format
lfs3_t lfs3;
@@ -1771,7 +1771,7 @@ code = '''
lfs3_unmount(&lfs3) => 0;
// reset badbit
lfs3_emubd_markgood(CFG, badblock) => 0;
lfs3_emubd_mkgood(CFG, badblock) => 0;
}
'''
@@ -1816,8 +1816,8 @@ code = '''
badbit_/8, badbit_%8);
// mark our badbits as bad
lfs3_emubd_markbadbit(CFG, BADBLOCK, badbit) => 0;
lfs3_emubd_markbadbit(CFG, BADBLOCK_, badbit_) => 0;
lfs3_emubd_mkbadbit(CFG, BADBLOCK, badbit) => 0;
lfs3_emubd_mkbadbit(CFG, BADBLOCK_, badbit_) => 0;
// keep track of open files so we clean up correctly
lfs3_file_t files[N];
@@ -1980,8 +1980,8 @@ code = '''
corrupt:;
// reset badbits
lfs3_emubd_markgood(CFG, BADBLOCK) => 0;
lfs3_emubd_markgood(CFG, BADBLOCK_) => 0;
lfs3_emubd_mkgood(CFG, BADBLOCK) => 0;
lfs3_emubd_mkgood(CFG, BADBLOCK_) => 0;
}
'''
@@ -2063,7 +2063,7 @@ code = '''
corrupt:;
// reset badbit
lfs3_emubd_markgood(CFG, BADBLOCK) => 0;
lfs3_emubd_mkgood(CFG, BADBLOCK) => 0;
}
'''
@@ -2171,7 +2171,7 @@ code = '''
lfs3_unmount(&lfs3) => 0;
// reset badbit
lfs3_emubd_markgood(CFG, badblock) => 0;
lfs3_emubd_mkgood(CFG, badblock) => 0;
}
'''
@@ -2282,7 +2282,7 @@ code = '''
lfs3_unmount(&lfs3) => 0;
// reset badbit
lfs3_emubd_markgood(CFG, badblock) => 0;
lfs3_emubd_mkgood(CFG, badblock) => 0;
}
'''
@@ -2346,7 +2346,7 @@ code = '''
(lfs3_size_t)BADBLOCK, badbit/8, badbit, badbit/8, badbit%8);
// mark our badbit as bad
lfs3_emubd_markbadbit(CFG, BADBLOCK, badbit) => 0;
lfs3_emubd_mkbadbit(CFG, BADBLOCK, badbit) => 0;
// With metastability, basically any filesystem operation can
// return LFS3_ERR_CORRUPT. This is ok, what we're really testing
@@ -2430,7 +2430,7 @@ code = '''
corrupt:;
// reset badbit
lfs3_emubd_markgood(CFG, BADBLOCK) => 0;
lfs3_emubd_mkgood(CFG, BADBLOCK) => 0;
}
'''
@@ -2504,7 +2504,7 @@ code = '''
badblock, badbit/8, badbit, badbit/8, badbit%8);
// mark our badbit as bad
lfs3_emubd_markbadbit(CFG, badblock, badbit) => 0;
lfs3_emubd_mkbadbit(CFG, badblock, badbit) => 0;
// With metastability, basically any filesystem operation can
// return LFS3_ERR_CORRUPT. This is ok, what we're really testing
@@ -2573,7 +2573,7 @@ code = '''
lfs3_unmount(&lfs3) => 0;
// reset badbit
lfs3_emubd_markgood(CFG, badblock) => 0;
lfs3_emubd_mkgood(CFG, badblock) => 0;
}
'''
@@ -2641,7 +2641,7 @@ code = '''
badblock, badbit/8, badbit, badbit/8, badbit%8);
// mark our badbit as bad
lfs3_emubd_markbadbit(CFG, badblock, badbit) => 0;
lfs3_emubd_mkbadbit(CFG, badblock, badbit) => 0;
// With metastability, basically any filesystem operation can
// return LFS3_ERR_CORRUPT. This is ok, what we're really testing
@@ -2710,7 +2710,7 @@ code = '''
lfs3_unmount(&lfs3) => 0;
// reset badbit
lfs3_emubd_markgood(CFG, badblock) => 0;
lfs3_emubd_mkgood(CFG, badblock) => 0;
}
'''
@@ -2818,7 +2818,7 @@ code = '''
// bit differently
// mark our badblock as bad
lfs3_emubd_markbad(CFG, badblock) => 0;
lfs3_emubd_mkbad(CFG, badblock) => 0;
// manually flipping? flip all badbits in badblocks
if (BADBLOCK_BEHAVIOR == LFS3_EMUBD_BADBLOCK_MANUAL) {
@@ -3136,7 +3136,7 @@ code = '''
// bit differently
// mark our badblock as bad
lfs3_emubd_markbad(CFG, badblock) => 0;
lfs3_emubd_mkbad(CFG, badblock) => 0;
// manually flipping? flip all badbits in badblocks
if (BADBLOCK_BEHAVIOR == LFS3_EMUBD_BADBLOCK_MANUAL) {
@@ -3552,7 +3552,7 @@ code = '''
// bit differently
// mark our badblock as bad
lfs3_emubd_markbad(CFG, badblock) => 0;
lfs3_emubd_mkbad(CFG, badblock) => 0;
// manually flipping? flip all badbits in badblocks
if (BADBLOCK_BEHAVIOR == LFS3_EMUBD_BADBLOCK_MANUAL) {
@@ -3837,7 +3837,7 @@ code = '''
// bit differently
// mark our badblock as bad
lfs3_emubd_markbad(CFG, badblock) => 0;
lfs3_emubd_mkbad(CFG, badblock) => 0;
// manually flipping? flip all badbits in badblocks
if (BADBLOCK_BEHAVIOR == LFS3_EMUBD_BADBLOCK_MANUAL) {
@@ -4441,7 +4441,7 @@ code = '''
// bit differently
// mark our badblock as bad
lfs3_emubd_markbad(CFG, badblock) => 0;
lfs3_emubd_mkbad(CFG, badblock) => 0;
// manually flipping? flip all badbits in badblocks
if (BADBLOCK_BEHAVIOR == LFS3_EMUBD_BADBLOCK_MANUAL) {