runners: emubd/kiwibd: Adopted emulated simtime API
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
+60
-15
@@ -436,9 +436,9 @@ FILE *bench_trace_file = NULL;
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uint32_t bench_trace_cycles = 0;
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uint64_t bench_trace_time = 0;
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uint64_t bench_trace_open_time = 0;
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lfs3_emubd_sleep_t bench_read_sleep = 0.0;
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lfs3_emubd_sleep_t bench_prog_sleep = 0.0;
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lfs3_emubd_sleep_t bench_erase_sleep = 0.0;
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lfs3_emubd_ns_t bench_read_sleep = 0.0;
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lfs3_emubd_ns_t bench_prog_sleep = 0.0;
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lfs3_emubd_ns_t bench_erase_sleep = 0.0;
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// this determines both the backtrace buffer and the trace printf buffer, if
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// trace ends up interleaved or truncated this may need to be increased
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@@ -604,9 +604,13 @@ void bench_permutation(size_t i, uint32_t *buffer, size_t size) {
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typedef struct bench_record {
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const char *m;
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uintmax_t n;
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lfs3_emubd_io_t last_reads;
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lfs3_emubd_io_t last_progs;
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lfs3_emubd_io_t last_erases;
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lfs3_emubd_io_t last_readed;
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lfs3_emubd_io_t last_proged;
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lfs3_emubd_io_t last_progged;
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lfs3_emubd_io_t last_erased;
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lfs3_emubd_ns_t last_simtime;
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} bench_record_t;
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static struct lfs3_cfg *bench_cfg = NULL;
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@@ -622,12 +626,20 @@ void bench_reset(struct lfs3_cfg *cfg) {
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void bench_start(const char *m, uintmax_t n) {
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// measure current read/prog/erase
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assert(bench_cfg);
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lfs3_emubd_sio_t reads = lfs3_emubd_reads(bench_cfg);
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assert(reads >= 0);
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lfs3_emubd_sio_t progs = lfs3_emubd_progs(bench_cfg);
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assert(progs >= 0);
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lfs3_emubd_sio_t erases = lfs3_emubd_erases(bench_cfg);
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assert(erases >= 0);
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lfs3_emubd_sio_t readed = lfs3_emubd_readed(bench_cfg);
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assert(readed >= 0);
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lfs3_emubd_sio_t proged = lfs3_emubd_proged(bench_cfg);
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assert(proged >= 0);
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lfs3_emubd_sio_t progged = lfs3_emubd_progged(bench_cfg);
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assert(progged >= 0);
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lfs3_emubd_sio_t erased = lfs3_emubd_erased(bench_cfg);
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assert(erased >= 0);
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// note this can error if no timings provided
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lfs3_emubd_sns_t simtime = lfs3_emubd_simtime(bench_cfg);
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// allocate a new record
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bench_record_t *record = mappend(
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@@ -637,31 +649,64 @@ void bench_start(const char *m, uintmax_t n) {
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&bench_record_capacity);
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record->m = m;
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record->n = n;
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record->last_reads = reads;
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record->last_progs = progs;
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record->last_erases = erases;
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record->last_readed = readed;
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record->last_proged = proged;
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record->last_progged = progged;
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record->last_erased = erased;
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record->last_simtime = simtime;
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}
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void bench_stop(const char *m) {
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// measure current read/prog/erase
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assert(bench_cfg);
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lfs3_emubd_sio_t reads = lfs3_emubd_reads(bench_cfg);
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assert(reads >= 0);
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lfs3_emubd_sio_t progs = lfs3_emubd_progs(bench_cfg);
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assert(progs >= 0);
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lfs3_emubd_sio_t erases = lfs3_emubd_erases(bench_cfg);
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assert(erases >= 0);
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lfs3_emubd_sio_t readed = lfs3_emubd_readed(bench_cfg);
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assert(readed >= 0);
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lfs3_emubd_sio_t proged = lfs3_emubd_proged(bench_cfg);
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assert(proged >= 0);
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lfs3_emubd_sio_t progged = lfs3_emubd_progged(bench_cfg);
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assert(progged >= 0);
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lfs3_emubd_sio_t erased = lfs3_emubd_erased(bench_cfg);
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assert(erased >= 0);
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// note this can error if no timings provided
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lfs3_emubd_sns_t simtime = lfs3_emubd_simtime(bench_cfg);
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// find our record
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for (size_t i = 0; i < bench_record_count; i++) {
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if (strcmp(bench_records[i].m, m) == 0) {
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// print results
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printf("benched %s %jd %"PRIu64" %"PRIu64" %"PRIu64"\n",
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bench_records[i].m,
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bench_records[i].n,
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readed - bench_records[i].last_readed,
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proged - bench_records[i].last_proged,
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erased - bench_records[i].last_erased);
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if (simtime >= 0) {
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printf("benched %s %jd "
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"%"PRIu64" %"PRIu64" %"PRIu64" "
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"%"PRIu64" %"PRIu64" %"PRIu64" "
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"%"PRIu64"\n",
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bench_records[i].m,
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bench_records[i].n,
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reads - bench_records[i].last_reads,
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progs - bench_records[i].last_progs,
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erases - bench_records[i].last_erases,
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readed - bench_records[i].last_readed,
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progged - bench_records[i].last_progged,
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erased - bench_records[i].last_erased,
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simtime - bench_records[i].last_simtime);
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} else {
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printf("benched %s %jd "
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"%"PRIu64" %"PRIu64" %"PRIu64" "
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"%"PRIu64" %"PRIu64" %"PRIu64"\n",
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bench_records[i].m,
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bench_records[i].n,
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reads - bench_records[i].last_reads,
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progs - bench_records[i].last_progs,
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erases - bench_records[i].last_erases,
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readed - bench_records[i].last_readed,
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progged - bench_records[i].last_progged,
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erased - bench_records[i].last_erased);
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}
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// remove our record
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memmove(&bench_records[i],
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