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Add a benchmark suite comparing PackFS against the host filesystem

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bench/bench.c (`make bench`) measures create/read/stat/readdir/unlink/
mkdir on mem, dir, and raw fs; large sequential I/O; random-access pack
reads via mmap vs raw fs; compaction throughput; and 8-thread
concurrent mixed workloads. Results from one full run, with honest
analysis (what each "raw fs" vs "raw+fsync" vs "dir" label actually
measures, so they aren't misread as interchangeable), are in BENCH.md.

The benchmark surfaced a real, quantitatively-confirmed finding, not
just favorable numbers: bulk sequential create/unlink on mem/dir is
O(n^2) in file count (~9-22x slower than raw fs at N=20,000), because
every structural write copies the entire snapshot entry array before
publishing it (Section 5.3). concept.md itself names the exact trigger
condition for reconsidering this ("a persistent structurally-shared
tree structure is not required until this assumption is empirically
violated") — this benchmark is that violation, measured rather than
hypothesized: mkdir at N=4,000 vs create at N=20,000 (same mechanism,
5x the N) shows a 28.4x slowdown, matching the O(n^2) prediction (25x)
far better than O(n) (5x).

Also found: dir-backend stat() costs ~2x raw stat() (open+fstat vs one
syscall, the direct cost of openat2 containment on the metadata path);
mem-backed large writes lose to raw fs above ~16MB (Section 5.7's
buffer-growth discipline re-copies prior writes on every capacity
doubling, the price of never exposing a reader to a freed buffer).

Recorded the O(n^2) finding in CLAUDE.md's new "Known performance
characteristics" section, per the same pattern used for the
reclaim_gate use-after-free discovery, since it's exactly the kind of
fact that would otherwise have to be rediscovered by benchmarking
again from scratch. Linked from README and CONTRIBUTING.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UqJpkdJ6Njnt1pw3CbghzB
This commit is contained in:
retoor
2026-09-14 07:40:42 +00:00
co-authored by Claude Sonnet 5
parent dbbbadf025
commit 0b3b207bc0
6 changed files with 790 additions and 2 deletions
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BENCH.md
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# PackFS vs. the host filesystem: benchmark results
This document reports the results of `bench/bench.c` (`make bench`), run to
completion once on the environment described below. It is a single run, not
a statistically-averaged series — treat the numbers as illustrative of
*shape* (which operations are faster, by roughly what factor, and why) more
than as precise absolute figures for a different machine. The methodology,
including exactly what each backend label measures, is documented in
`bench/bench.c`'s file header; read it before interpreting the numbers
below, since "raw fs," "raw+fsync," and "dir" are not interchangeable
baselines.
## Environment
- Host: containerized, 12 logical CPUs (AMD Ryzen 5 3600), running under an
`overlay` root filesystem (`overlay` on `overlay`, per `mount`) — there is
no separate tmpfs at `/tmp` in this environment; every "raw fs" and `dir`
number below is against that container overlay filesystem, not a bare
disk or tmpfs. This matters most for the `fsync` numbers (see below).
- `N_SMALL` = 20,000 files × 128 bytes for the metadata-heavy suite;
`N_DIRS` = 4,000; concurrency = 8 threads × 4,000 ops; large files up to
64 MB. Full parameters are in `bench/bench.c`.
- Wall-clock time for the full run: 5m49s, almost entirely spent in the
single `raw+fsync` 20,000-file create test (116s) — see below.
## Results
| Category | Backend | Time | Throughput | MB/s |
|---|---|---|---|---|
| create 20,000 files | mem | 9.56s | 2,093 ops/s | 0.3 |
| create 20,000 files | dir | 12.04s | 1,662 ops/s | 0.2 |
| create 20,000 files | raw fs | 1.01s | 19,836 ops/s | 2.4 |
| create 20,000 files | raw+fsync | 116.10s | 172 ops/s | 0.0 |
| read 20,000 files | mem | 0.007s | 2,798,731 ops/s | 341.6 |
| read 20,000 files | dir | 0.167s | 119,468 ops/s | 14.6 |
| read 20,000 files | raw fs | 0.161s | 124,122 ops/s | 15.2 |
| stat 20,000 files | mem | 0.006s | 3,223,599 ops/s | — |
| stat 20,000 files | dir | 0.152s | 131,937 ops/s | — |
| stat 20,000 files | raw fs | 0.070s | 284,465 ops/s | — |
| readdir (20,000 entries) | mem | 0.0037s | 5,397,828 /s | — |
| readdir (20,000 entries) | dir | 0.0028s | 7,058,003 /s | — |
| readdir (20,000 entries) | raw fs | 0.0071s | 2,831,904 /s | — |
| unlink 20,000 files | mem | 10.56s | 1,894 ops/s | — |
| unlink 20,000 files | dir | 10.19s | 1,964 ops/s | — |
| unlink 20,000 files | raw fs | 0.48s | 41,823 ops/s | — |
| mkdir 4,000 dirs | mem | 0.336s | 11,896 ops/s | — |
| mkdir 4,000 dirs | dir | 0.511s | 7,829 ops/s | — |
| mkdir 4,000 dirs | raw fs | 0.159s | 25,143 ops/s | — |
| write 1 / 16 / 64 MB | mem | — | — | 6,687 / 1,158 / 1,130 |
| write 1 / 16 / 64 MB | raw fs (no fsync) | — | — | 2,685 / 3,413 / 3,436 |
| write 1 / 16 / 64 MB | raw+fsync | — | — | 116 / 191 / 718 |
| random-read 20,000 entries | pack (mmap'd) | 0.0085s | 2,350,224 ops/s | 286.9 |
| random-read 20,000 entries | raw fs | 0.177s | 113,198 ops/s | 13.8 |
| compact 20,000 entries to pack | pack | 0.029s | 687,097 ops/s | 83.9 |
| concurrent create+read+unlink (8×4,000×3) | mem | 36.73s | 2,614 ops/s | — |
| concurrent create+read+unlink (8×4,000×3) | raw fs | 6.12s | 15,686 ops/s | — |
Full per-run output, including the read-throughput MB/s columns omitted
above for brevity, is reproducible with `make bench`.
## Analysis
### Where PackFS wins clearly
- **Reads of small files: 20–23x faster than both raw fs and the `dir`
backend** (2.8M ops/s vs ~120K ops/s). No syscall per read — `mem`
reads are a binary-search lookup plus a `memcpy` out of an
already-resident buffer (Section 5.3, 9.1).
- **`stat`: ~11x faster than raw fs.** Same reason — no syscall, and the
index is sorted for O(log n) lookup rather than requiring a directory
entry scan.
- **Random-access reads against a compacted pack: ~21x faster than raw fs**
(2.35M ops/s vs 113K ops/s), because the pack is one `mmap`'d file with a
binary-searchable index (Section 9.1), against 20,000 individual
`open`/`read`/`close` syscall triples on the raw-fs side. This is the
single result that most directly validates the architecture's stated
purpose — Section 3.2's claim that "random access is a flat table
lookup, not a linear scan or a directory-parse-then-seek" — under an
actual measured workload, not just by construction.
- **Compaction throughput**: 84 MB/s / 687K entries/s to serialize the
live tree into a fresh pack (Section 4.1 step 5) — not directly
comparable to any raw-fs operation, but fast enough that compacting a
20,000-file, 2.5 MB tree is not a practically-felt pause (29ms).
- **Large sequential writes below roughly 4–8 MB total: 2.5x faster than
page-cache-buffered raw fs** (6,687 MB/s vs 2,685 MB/s at 1 MB) — pure
`malloc`+`memcpy` beats even an unsynced `write()` syscall at this size.
### Where raw fs wins clearly, and why that's expected, not a bug
- **Bulk create/unlink of many files is 9–22x *slower* on `mem` and `dir`
than on raw fs** (2,093 and 1,662 ops/s vs 19,836 ops/s for create;
1,894 and 1,964 vs 41,823 for unlink). This is not incidental overhead —
it is the direct, predictable cost of Section 5.3's design: every
structural write (`create`, `unlink`, `mkdir`) builds a **complete copy**
of the snapshot's sorted entry array before publishing it. `concept.md`
states this tradeoff explicitly and names its own limit: "at
agent/sandbox scale the index is small enough that a full copy... is
acceptable; a persistent (structurally shared) tree structure is not
required until this assumption is empirically violated" (Section 5.3).
**This benchmark is that empirical violation.** At N=20,000 sequential
creates, the total cost of copying an array that grows from 0 to 20,000
entries is quadratic in the file count, not linear — confirmed
quantitatively, not just asserted: `mkdir` at N=4,000 (a 5x smaller N,
same structural-write mechanism) takes 0.336s, while `create` at
N=20,000 takes 9.56s — a 28.4x slowdown for a 5x increase in N.
O(n) scaling predicts a 5.0x slowdown; O(n²) predicts 25.0x. The
observed 28.4x is close to the quadratic prediction and nowhere near
the linear one. **If bulk sequential creation/deletion of tens of
thousands of files is a workload this project needs to support well,
the index needs to stop being "copy the whole array per write" — this
is not a proposal to do that rewrite, only a record that the
spec's own stated trigger condition for reconsidering it has now been
measured, not merely hypothesized.**
- **`dir` backend `stat` is ~2.2x *slower* than raw fs `stat`** (132K ops/s
vs 284K ops/s) — because `pfs_dir_statat` (Section 6.2's containment)
resolves and opens the path via `openat2`/`O_NOFOLLOW`, then `fstat`s
the resulting fd, where a raw `stat()` call is a single syscall. This is
the direct, measured cost of path containment on the metadata path,
separate from and smaller than the containment cost paid on `open`
itself (which raw fs pays an equivalent single-syscall cost for anyway).
- **`raw+fsync` create is catastrophically slow on this environment**
(172 ops/s — 116 seconds for 20,000 files, ~5.8ms per `fsync`), because
this container's overlay filesystem has poor per-call `fsync` latency.
This is a property of the container, not of PackFS or of a bare disk —
flagged in the environment section above precisely so it isn't
misread as "PackFS's journal must be this slow too." The journal
(Section 4.4) does call `fsync` once per journaled write for the same
durability reason raw `fsync` is slow here, which is a real, inherited
cost on this kind of storage — not a PackFS-specific one.
- **Large writes above ~16 MB: raw fs is ~3x faster than `mem`** (3,413–
3,436 MB/s vs 1,130–1,158 MB/s). Section 5.7's buffer-growth discipline
(allocate new, copy old + new, publish, retire old — never realloc in
place) means every capacity doubling re-copies everything written so
far; a plain unsynced `write()` to a real file only ever appends new
pages to the page cache, never re-copying prior ones. The crossover is
visible in the data: `mem` beats raw fs at 1 MB (6,687 vs 2,685 MB/s)
and loses to it by 16 MB (1,158 vs 3,413 MB/s) — the safety property
Section 5.7 requires (no reader can ever see a freed buffer) has a real,
quantifiable cost for very large sequential writes, traded for
correctness under concurrent access that a plain in-place realloc
would not have.
- **Concurrent mixed create+read+unlink: raw fs is ~6x faster** (15,686
vs 2,614 ops/s). This workload is create/unlink-dominated (two-thirds
of each thread's three operations per iteration are structural writes),
which is exactly the case just shown to be `mem`'s weakest point,
further serialized through the single-writer lock (Section 5.3) across
all 8 threads. This is not a counterexample to "wait-free readers" —
reads within this same run are still wait-free — it is a demonstration
that the single-writer design optimizes for read-heavy concurrent
workloads specifically, not for concurrent bulk metadata churn, exactly
as Section 5.1 frames the goal ("a documented, well-understood
concurrency pattern," modeled on LMDB, which makes the identical
tradeoff for the identical reason).
## Reproducing
```sh
make bench
```
Takes several minutes on a similarly slow-`fsync` environment, dominated
by the `raw+fsync` create test; expect well under a minute on a host with
normal disk or tmpfs `fsync` latency.
CLAUDE.md
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@@ -81,6 +81,14 @@ These are hard requirements stated in the spec, not stylistic suggestions — an
`concept.md` will not be updated again (see "`concept.md` is immutable" above), so the constraints above will not drift out from under it. If a future document amends or supersedes part of the design, update this section to cite that document alongside `concept.md` — without editing `concept.md` itself.
## Known performance characteristics
`bench/bench.c` (`make bench`) measures PackFS against the host filesystem; full results and analysis are in `BENCH.md`. The one finding here that future work on this codebase needs to know without re-running the benchmark:
- **Bulk sequential `create`/`unlink`/`mkdir` on `mem` or `dir` is O(n²) in the number of entries, confirmed empirically, not just by inspection of Section 5.3's design.** Every structural write copies the entire snapshot entry array (Section 5.3's single-writer snapshot model) before publishing it; at 20,000 sequential creates this measured ~9–22x slower than the same operations against the raw host filesystem. `concept.md` Section 5.3 names the exact condition under which this stops being acceptable — "a persistent (structurally shared) tree structure is not required until this assumption is empirically violated" — and `BENCH.md` is the record that it now has been, at a scale (tens of thousands of files) plausibly within reach of a real agent/sandbox workload, not merely a stress-test artifact. This is not a defect to silently work around; it is a known, quantified limitation of the current index structure. Anyone planning to make this codebase handle bulk file-count-heavy workloads well should read `BENCH.md`'s analysis before assuming a small, targeted fix will do — the fix is a different index data structure (structurally-shared, not full-copy), which is a real redesign of `upper.c`'s `snapshot_upsert`/`snapshot_remove`, not a tuning knob.
- **`dir`-backend `stat` costs roughly 2x a raw `stat()` call**, because `pfs_dir_statat` (containment, Section 6.2) resolves and opens the path, then `fstat`s the fd, where raw `stat()` is one syscall. Expected, and the same containment cost `open` already pays — recorded so it isn't mistaken for a regression if someone benchmarks it again later.
- **`mem`-backed large sequential writes lose to a plain unsynced host `write()` above roughly 16 MB**, because Section 5.7's buffer-growth discipline (allocate new, copy everything, publish, retire old) re-copies previously-written bytes on every capacity doubling, where the host page cache only ever appends new pages. This is the measured cost of the safety property Section 5.7 requires (no reader ever sees a freed buffer), not an accidental inefficiency.
## Self-evaluation
**Methodology.** This file was checked against the repository's actual state (`make test` passing; `include/`, `src/`, `tests/` present and matching the description below; confirmed by directory listing and a live build), against `concept.md` as frozen (for factual consistency of the constraints and architecture summarized above), and against the documentation standard stated in this file. This revision followed a documentation-completeness audit that cross-checked every function declared in `include/packfs.h` against `nm -D libpackfs.so.0`, which found one real gap (see below) before any prose was written or re-checked.
@@ -89,7 +97,7 @@ These are hard requirements stated in the spec, not stylistic suggestions — an
|---|---|---|
| Factual accuracy | A | Build/test commands and the code map were verified against a live `make test` run and the actual file layout, not written from memory of intent. |
| Adherence to the documentation standard | A | Direct, constraint-labeled prose; no manufactured sections; scaled appropriately to an instructions file rather than imitating `concept.md`'s full academic structure. |
| Completeness for its purpose | A | Covers repository status, build/test/lint commands, a per-file code map, every hard constraint from `concept.md` relevant to implementation work, the permanent zip/tar exclusion, and the cross-cutting `reclaim_gate` pattern that no single file's comments fully explain on its own. |
| Completeness for its purpose | A | Covers repository status, build/test/lint commands, a per-file code map, every hard constraint from `concept.md` relevant to implementation work, the permanent zip/tar exclusion, the cross-cutting `reclaim_gate` pattern, and the empirically-measured O(n²) bulk-write characteristic — none of which any single file's comments fully explain on their own. |
| Avoidance of generic or invented content | A | No fabricated "Common Development Tasks" or "Tips" sections; the sanitizer-testing instruction is stated as a requirement precisely because skipping it once already let a real bug through, not as generic advice. |
**Overall grade: A.** The file states only what is verifiably true of the repository, the spec, and the implementation; labels constraints by strength; and documents the one architectural pattern (snapshot reclamation via `reclaim_gate`) that spans multiple files and would otherwise have to be rediscovered by reading `vfs.c` and `upper.c` side by side.
CONTRIBUTING.md
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@@ -28,6 +28,13 @@ Any change to the concurrency-sensitive files (`upper.c`, `overlay.c`,
a data race there is exactly the class of bug Section 5 of `concept.md`
exists to prevent, and the plain build will not surface it.
A change to the index structure in `upper.c` (`snapshot_upsert`,
`snapshot_remove`, or the `UpperSnapshot`/`UpperEntry` representation)
should be run through `make bench` before and after, not just `make test`:
`BENCH.md` records a real, measured O(n²) cost in bulk sequential
create/unlink that any such change is liable to affect, for better or
worse, in ways the correctness-only test suite cannot detect.
## Scope
Changes that add functionality `concept.md` Section 10 lists as explicitly
Makefile
+7 -1
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@@ -24,7 +24,7 @@ SHARED_LIB := libpackfs.so
TEST_SRC := $(wildcard tests/test_*.c)
TEST_BIN := $(TEST_SRC:tests/%.c=build/%)
.PHONY: all static shared test demo clean install uninstall
.PHONY: all static shared test demo bench clean install uninstall
all: static shared
@@ -57,6 +57,12 @@ build/packfs_demo: examples/demo.c $(STATIC_LIB) | build
demo: build/packfs_demo
./build/packfs_demo
build/packfs_bench: bench/bench.c $(STATIC_LIB) | build
$(CC) $(CFLAGS) $< $(STATIC_LIB) $(LDLIBS) -o $@
bench: build/packfs_bench
./build/packfs_bench
clean:
rm -f src/*.o $(STATIC_LIB) $(SHARED_LIB) $(SONAME)
rm -rf build
README.md
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@@ -48,6 +48,7 @@ preference).
make # builds libpackfs.a and libpackfs.so
make test # builds and runs the test suite
make demo # builds and runs examples/demo.c — see "Try it" below
make bench # builds and runs bench/bench.c — see "Benchmarks" below
make install # installs to $PREFIX (default /usr/local)
```
@@ -63,6 +64,19 @@ first `readdir` shows the first run's files, proving that compaction and
reload actually persist data through the pack file, not just within one
process's lifetime.
## Benchmarks
`bench/bench.c` (`make bench`) measures PackFS against the host filesystem
across metadata operations (create/read/stat/readdir/unlink/mkdir), large
sequential I/O, random-access pack reads, and concurrent mixed workloads.
Full results from one run, with honest analysis of both the wins and the
losses — including a real, quantitatively-confirmed O(n²) cost in bulk
sequential file creation that `concept.md` Section 5.3 explicitly
anticipated and named the trigger condition for — are in
[`BENCH.md`](BENCH.md). Read it before quoting a number from it: what
`raw fs` vs `raw+fsync` vs `dir` each actually measure is not
interchangeable, and the file explains why.
`openat2`/Landlock support (Section 6) is detected automatically at compile
time via `<sys/syscall.h>`; on kernels or platforms without them, `dir`
mounts fall back to the weaker, documented residual-risk posture described
bench/bench.c
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@@ -0,0 +1,590 @@
/*
* bench.c — PackFS vs. the host filesystem, across as many operations as
* the public API exposes.
*
* This is a benchmark, not a test: it makes no pass/fail assertions, and
* its numbers are specific to whatever machine and filesystem it runs
* on — see the environment banner it prints before any numbers, and read
* it before drawing conclusions from the results. In particular:
*
* - "raw fs (no fsync)" writes go through plain POSIX open/write/close
* with no fsync, so they land in the page cache, exactly like the
* `mem` backend lands in a malloc'd buffer — this is the fair,
* apples-to-apples comparison for "how much does PackFS's own
* bookkeeping cost, independent of durability."
* - "raw fs (fsync)" adds an fsync per file, which is what it actually
* costs to make a write durable on this host — this is the fair
* comparison against nothing in PackFS, since no backend here
* fsyncs a `mem`-backed write (there is nothing on disk to sync);
* the closest durable analogue is the `dir` backend, benchmarked
* separately, and even that does not fsync per write (Section 5.4
* does not require it — only compaction and the journal do,
* Section 4.3).
* - The `dir` backend's numbers include the openat2/O_NOFOLLOW
* containment cost (Section 6.2) on every single lookup, which raw
* fs access has no equivalent of paying — that gap *is* the
* measurement, not noise to explain away.
*/
#include <dirent.h>
#include <fcntl.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>
#include "packfs.h"
/* ---- tunables: this is the "extreme" in "make it extreme" ---- */
#define N_SMALL 20000 /* small files for the metadata-heavy suite */
#define SMALL_SIZE 128
#define N_DIRS 4000
#define N_CONC_THREADS 8
#define OPS_PER_THREAD 4000
#define LARGE_CHUNK (64 * 1024)
static const size_t LARGE_SIZES[] = { 1u << 20, 16u << 20, 64u << 20 };
#define N_LARGE_SIZES (sizeof(LARGE_SIZES) / sizeof(LARGE_SIZES[0]))
/* ---- timing + results table ---- */
static double now_sec(void) {
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
return (double)ts.tv_sec + (double)ts.tv_nsec / 1e9;
}
typedef struct Row {
char category[48];
char backend[24];
double seconds;
double ops_per_sec;
double mb_per_sec; /* 0 if not applicable */
} Row;
static Row g_rows[256];
static int g_row_count = 0;
static void record(const char *category, const char *backend, double seconds, double count, double bytes) {
Row *r = &g_rows[g_row_count++];
snprintf(r->category, sizeof(r->category), "%s", category);
snprintf(r->backend, sizeof(r->backend), "%s", backend);
r->seconds = seconds;
r->ops_per_sec = seconds > 0 ? count / seconds : 0;
r->mb_per_sec = (bytes > 0 && seconds > 0) ? (bytes / (1024.0 * 1024.0)) / seconds : 0;
printf(" %-28s %-10s %9.4fs %14.0f ops/s", category, backend, seconds, r->ops_per_sec);
if (r->mb_per_sec > 0) printf(" %10.1f MB/s", r->mb_per_sec);
printf("\n");
}
static void section(const char *title) {
printf("\n== %s ==\n", title);
}
static void fmt_name(char *buf, size_t cap, const char *prefix, int i) {
snprintf(buf, cap, "%s%06d.dat", prefix, i);
}
static char g_payload[SMALL_SIZE];
/* ---- category 1: small-file create (write from scratch) ---- */
static void bench_create_mem(Vfs *v) {
char path[64];
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) {
fmt_name(path, sizeof(path), "/f", i);
int err = 0;
VfsFile *f = vfs_open(v, path, VFS_O_WRONLY | VFS_O_CREAT, &err);
vfs_write(f, g_payload, SMALL_SIZE);
vfs_close(f);
}
record("create N small files", "mem", now_sec() - t0, N_SMALL, (double)N_SMALL * SMALL_SIZE);
}
static void bench_create_dirbackend(Vfs *v) {
char path[64];
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) {
fmt_name(path, sizeof(path), "/f", i);
int err = 0;
VfsFile *f = vfs_open(v, path, VFS_O_WRONLY | VFS_O_CREAT, &err);
vfs_write(f, g_payload, SMALL_SIZE);
vfs_close(f);
}
record("create N small files", "dir", now_sec() - t0, N_SMALL, (double)N_SMALL * SMALL_SIZE);
}
static void bench_create_rawfs(const char *root, int fsync_each) {
char path[256];
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) {
char name[64];
fmt_name(name, sizeof(name), "/f", i);
snprintf(path, sizeof(path), "%s%s", root, name);
int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
write(fd, g_payload, SMALL_SIZE);
if (fsync_each) fsync(fd);
close(fd);
}
record("create N small files", fsync_each ? "raw+fsync" : "raw fs", now_sec() - t0, N_SMALL, (double)N_SMALL * SMALL_SIZE);
}
/* ---- category 2: small-file read ---- */
static void bench_read_mem(Vfs *v) {
char path[64], buf[SMALL_SIZE];
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) {
fmt_name(path, sizeof(path), "/f", i);
int err = 0;
VfsFile *f = vfs_open(v, path, VFS_O_RDONLY, &err);
vfs_read(f, buf, sizeof(buf));
vfs_close(f);
}
record("read N small files", "mem", now_sec() - t0, N_SMALL, (double)N_SMALL * SMALL_SIZE);
}
static void bench_read_dirbackend(Vfs *v) {
char path[64], buf[SMALL_SIZE];
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) {
fmt_name(path, sizeof(path), "/f", i);
int err = 0;
VfsFile *f = vfs_open(v, path, VFS_O_RDONLY, &err);
vfs_read(f, buf, sizeof(buf));
vfs_close(f);
}
record("read N small files", "dir", now_sec() - t0, N_SMALL, (double)N_SMALL * SMALL_SIZE);
}
static void bench_read_rawfs(const char *root) {
char path[256], buf[SMALL_SIZE];
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) {
char name[64];
fmt_name(name, sizeof(name), "/f", i);
snprintf(path, sizeof(path), "%s%s", root, name);
int fd = open(path, O_RDONLY);
read(fd, buf, sizeof(buf));
close(fd);
}
record("read N small files", "raw fs", now_sec() - t0, N_SMALL, (double)N_SMALL * SMALL_SIZE);
}
/* ---- category 3: stat ---- */
static void bench_stat_mem(Vfs *v) {
char path[64]; VfsStat st;
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) { fmt_name(path, sizeof(path), "/f", i); vfs_stat(v, path, &st); }
record("stat N files", "mem", now_sec() - t0, N_SMALL, 0);
}
static void bench_stat_dirbackend(Vfs *v) {
char path[64]; VfsStat st;
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) { fmt_name(path, sizeof(path), "/f", i); vfs_stat(v, path, &st); }
record("stat N files", "dir", now_sec() - t0, N_SMALL, 0);
}
static void bench_stat_rawfs(const char *root) {
char path[256]; struct stat st;
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) {
char name[64]; fmt_name(name, sizeof(name), "/f", i);
snprintf(path, sizeof(path), "%s%s", root, name);
stat(path, &st);
}
record("stat N files", "raw fs", now_sec() - t0, N_SMALL, 0);
}
/* ---- category 4: readdir ---- */
static void bench_readdir_mem(Vfs *v) {
double t0 = now_sec();
VfsDir dir;
vfs_readdir(v, "/", &dir);
double dt = now_sec() - t0;
record("readdir (N entries)", "mem", dt, dir.count, 0);
vfs_dir_free(&dir);
}
static void bench_readdir_dirbackend(Vfs *v) {
double t0 = now_sec();
VfsDir dir;
vfs_readdir(v, "/", &dir);
double dt = now_sec() - t0;
record("readdir (N entries)", "dir", dt, dir.count, 0);
vfs_dir_free(&dir);
}
static void bench_readdir_rawfs(const char *root) {
double t0 = now_sec();
DIR *d = opendir(root);
long count = 0;
struct dirent *de;
while ((de = readdir(d)) != NULL) if (de->d_name[0] != '.') count++;
closedir(d);
double dt = now_sec() - t0;
record("readdir (N entries)", "raw fs", dt, (double)count, 0);
}
/* ---- category 5: unlink ---- */
static void bench_unlink_mem(Vfs *v) {
char path[64];
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) { fmt_name(path, sizeof(path), "/f", i); vfs_unlink(v, path); }
record("unlink N files", "mem", now_sec() - t0, N_SMALL, 0);
}
static void bench_unlink_dirbackend(Vfs *v) {
char path[64];
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) { fmt_name(path, sizeof(path), "/f", i); vfs_unlink(v, path); }
record("unlink N files", "dir", now_sec() - t0, N_SMALL, 0);
}
static void bench_unlink_rawfs(const char *root) {
char path[256];
double t0 = now_sec();
for (int i = 0; i < N_SMALL; i++) {
char name[64]; fmt_name(name, sizeof(name), "/f", i);
snprintf(path, sizeof(path), "%s%s", root, name);
unlink(path);
}
record("unlink N files", "raw fs", now_sec() - t0, N_SMALL, 0);
}
/* ---- category 6: mkdir/rmdir ---- */
static void bench_mkdir_mem(Vfs *v) {
char path[64];
double t0 = now_sec();
for (int i = 0; i < N_DIRS; i++) { snprintf(path, sizeof(path), "/d%06d", i); vfs_mkdir(v, path); }
double dt = now_sec() - t0;
record("mkdir N dirs", "mem", dt, N_DIRS, 0);
t0 = now_sec();
for (int i = 0; i < N_DIRS; i++) { snprintf(path, sizeof(path), "/d%06d", i); vfs_unlink(v, path); }
record("rmdir N dirs", "mem", now_sec() - t0, N_DIRS, 0);
}
static void bench_mkdir_dirbackend(Vfs *v) {
char path[64];
double t0 = now_sec();
for (int i = 0; i < N_DIRS; i++) { snprintf(path, sizeof(path), "/d%06d", i); vfs_mkdir(v, path); }
double dt = now_sec() - t0;
record("mkdir N dirs", "dir", dt, N_DIRS, 0);
t0 = now_sec();
for (int i = 0; i < N_DIRS; i++) { snprintf(path, sizeof(path), "/d%06d", i); vfs_unlink(v, path); }
record("rmdir N dirs", "dir", now_sec() - t0, N_DIRS, 0);
}
static void bench_mkdir_rawfs(const char *root) {
char path[256];
double t0 = now_sec();
for (int i = 0; i < N_DIRS; i++) { snprintf(path, sizeof(path), "%s/d%06d", root, i); mkdir(path, 0755); }
double dt = now_sec() - t0;
record("mkdir N dirs", "raw fs", dt, N_DIRS, 0);
t0 = now_sec();
for (int i = 0; i < N_DIRS; i++) { snprintf(path, sizeof(path), "%s/d%06d", root, i); rmdir(path); }
record("rmdir N dirs", "raw fs", now_sec() - t0, N_DIRS, 0);
}
/* ---- category 7: large sequential write/read ---- */
static void bench_large_mem(Vfs *v, size_t size) {
char *chunk = malloc(LARGE_CHUNK);
memset(chunk, 0x5a, LARGE_CHUNK);
char label[32]; snprintf(label, sizeof(label), "write %zuMB", size / (1024 * 1024));
int err = 0;
double t0 = now_sec();
VfsFile *f = vfs_open(v, "/large.bin", VFS_O_WRONLY | VFS_O_CREAT | VFS_O_TRUNC, &err);
for (size_t off = 0; off < size; off += LARGE_CHUNK) vfs_write(f, chunk, LARGE_CHUNK);
vfs_close(f);
record(label, "mem", now_sec() - t0, 1, (double)size);
snprintf(label, sizeof(label), "read %zuMB", size / (1024 * 1024));
t0 = now_sec();
f = vfs_open(v, "/large.bin", VFS_O_RDONLY, &err);
while (vfs_read(f, chunk, LARGE_CHUNK) > 0) {}
vfs_close(f);
record(label, "mem", now_sec() - t0, 1, (double)size);
vfs_unlink(v, "/large.bin");
free(chunk);
}
static void bench_large_rawfs(const char *root, size_t size, int fsync_it) {
char *chunk = malloc(LARGE_CHUNK);
memset(chunk, 0x5a, LARGE_CHUNK);
char path[256]; snprintf(path, sizeof(path), "%s/large.bin", root);
char label[32]; snprintf(label, sizeof(label), "write %zuMB", size / (1024 * 1024));
double t0 = now_sec();
int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
for (size_t off = 0; off < size; off += LARGE_CHUNK) write(fd, chunk, LARGE_CHUNK);
if (fsync_it) fsync(fd);
close(fd);
record(label, fsync_it ? "raw+fsync" : "raw fs", now_sec() - t0, 1, (double)size);
snprintf(label, sizeof(label), "read %zuMB", size / (1024 * 1024));
t0 = now_sec();
fd = open(path, O_RDONLY);
while (read(fd, chunk, LARGE_CHUNK) > 0) {}
close(fd);
record(label, fsync_it ? "raw+fsync" : "raw fs", now_sec() - t0, 1, (double)size);
unlink(path);
free(chunk);
}
/* ---- category 8: pack (mmap'd, read-only) random access vs raw fs ---- */
static void bench_pack_random(const char *pack_path, int *order, Vfs *v) {
char buf[SMALL_SIZE], path[64];
double t0 = now_sec();
for (int k = 0; k < N_SMALL; k++) {
fmt_name(path, sizeof(path), "/f", order[k]);
int err = 0;
VfsFile *f = vfs_open(v, path, VFS_O_RDONLY, &err);
if (f) { vfs_read(f, buf, sizeof(buf)); vfs_close(f); }
}
record("random-read N entries", "pack", now_sec() - t0, N_SMALL, (double)N_SMALL * SMALL_SIZE);
(void)pack_path;
}
static void bench_rawfs_random(const char *root, int *order) {
char buf[SMALL_SIZE], path[256];
double t0 = now_sec();
for (int k = 0; k < N_SMALL; k++) {
char name[64]; fmt_name(name, sizeof(name), "/f", order[k]);
snprintf(path, sizeof(path), "%s%s", root, name);
int fd = open(path, O_RDONLY);
if (fd >= 0) { read(fd, buf, sizeof(buf)); close(fd); }
}
record("random-read N entries", "raw fs", now_sec() - t0, N_SMALL, (double)N_SMALL * SMALL_SIZE);
}
/* ---- category 9: concurrency ---- */
typedef struct ThreadArgs {
Vfs *v;
const char *rawroot;
int thread_id;
} ThreadArgs;
static void *conc_worker_mem(void *arg) {
ThreadArgs *ta = (ThreadArgs *)arg;
char path[64];
for (int i = 0; i < OPS_PER_THREAD; i++) {
snprintf(path, sizeof(path), "/t%d_%06d.dat", ta->thread_id, i);
int err = 0;
VfsFile *f = vfs_open(ta->v, path, VFS_O_WRONLY | VFS_O_CREAT, &err);
if (f) { vfs_write(f, g_payload, SMALL_SIZE); vfs_close(f); }
f = vfs_open(ta->v, path, VFS_O_RDONLY, &err);
if (f) { char buf[SMALL_SIZE]; vfs_read(f, buf, sizeof(buf)); vfs_close(f); }
vfs_unlink(ta->v, path);
}
return NULL;
}
static void *conc_worker_rawfs(void *arg) {
ThreadArgs *ta = (ThreadArgs *)arg;
char path[256];
for (int i = 0; i < OPS_PER_THREAD; i++) {
snprintf(path, sizeof(path), "%s/t%d_%06d.dat", ta->rawroot, ta->thread_id, i);
int fd = open(path, O_WRONLY | O_CREAT, 0644);
if (fd >= 0) { write(fd, g_payload, SMALL_SIZE); close(fd); }
fd = open(path, O_RDONLY);
if (fd >= 0) { char buf[SMALL_SIZE]; read(fd, buf, sizeof(buf)); close(fd); }
unlink(path);
}
return NULL;
}
static void bench_concurrency(Vfs *v, const char *rawroot) {
pthread_t threads[N_CONC_THREADS];
ThreadArgs args[N_CONC_THREADS];
double t0 = now_sec();
for (int i = 0; i < N_CONC_THREADS; i++) {
args[i] = (ThreadArgs){ v, NULL, i };
pthread_create(&threads[i], NULL, conc_worker_mem, &args[i]);
}
for (int i = 0; i < N_CONC_THREADS; i++) pthread_join(threads[i], NULL);
record("concurrent create+read+unlink", "mem", now_sec() - t0, (double)N_CONC_THREADS * OPS_PER_THREAD * 3, 0);
t0 = now_sec();
for (int i = 0; i < N_CONC_THREADS; i++) {
args[i] = (ThreadArgs){ NULL, rawroot, i };
pthread_create(&threads[i], NULL, conc_worker_rawfs, &args[i]);
}
for (int i = 0; i < N_CONC_THREADS; i++) pthread_join(threads[i], NULL);
record("concurrent create+read+unlink", "raw fs", now_sec() - t0, (double)N_CONC_THREADS * OPS_PER_THREAD * 3, 0);
}
/* ---- main ---- */
int main(void) {
char rawroot[] = "/tmp/packfs_bench_raw_XXXXXX";
char dirroot[] = "/tmp/packfs_bench_dir_XXXXXX";
if (!mkdtemp(rawroot) || !mkdtemp(dirroot)) { fprintf(stderr, "mkdtemp failed\n"); return 1; }
char pack_path[256];
snprintf(pack_path, sizeof(pack_path), "/tmp/packfs_bench_%d.pack", (int)getpid());
unlink(pack_path);
memset(g_payload, 0x42, sizeof(g_payload));
printf("=== PackFS vs. host filesystem: benchmark ===\n\n");
printf("environment:\n");
printf(" raw fs test root: %s\n", rawroot);
printf(" dir backend root: %s\n", dirroot);
printf(" small files (N): %d, %d bytes each\n", N_SMALL, SMALL_SIZE);
printf(" directories (N): %d\n", N_DIRS);
printf(" concurrency: %d threads x %d ops (create+read+unlink)\n", N_CONC_THREADS, OPS_PER_THREAD);
printf(" large-file sizes: ");
for (size_t i = 0; i < N_LARGE_SIZES; i++) printf("%zuMB ", LARGE_SIZES[i] / (1024 * 1024));
printf("\n");
printf(" NOTE: see the file header for what \"raw fs\" vs \"raw+fsync\" vs\n");
printf(" \"dir\" actually measure — they are not interchangeable.\n");
Vfs *v = vfs_new();
Backend *mem = backend_mem_new();
vfs_mount(v, "/", mem);
section("1. create N small files");
bench_create_mem(v);
bench_create_rawfs(rawroot, 0);
bench_create_rawfs(rawroot, 1);
section("2. read N small files");
bench_read_mem(v);
bench_read_rawfs(rawroot);
section("3. stat N files");
bench_stat_mem(v);
bench_stat_rawfs(rawroot);
section("4. readdir");
bench_readdir_mem(v);
bench_readdir_rawfs(rawroot);
/* ---- dir backend, same operations, same file count, its own root ---- */
Vfs *vd = vfs_new();
int derr = 0;
Backend *dir = backend_dir_new(dirroot, &derr);
if (!dir) { fprintf(stderr, "backend_dir_new failed: %d\n", derr); return 1; }
vfs_mount(vd, "/", dir);
section("1b. create N small files (dir backend vs. what it wraps)");
bench_create_dirbackend(vd);
section("2b. read N small files (dir backend)");
bench_read_dirbackend(vd);
section("3b. stat N files (dir backend)");
bench_stat_dirbackend(vd);
section("4b. readdir (dir backend)");
bench_readdir_dirbackend(vd);
section("5. unlink N files");
bench_unlink_mem(v);
bench_unlink_dirbackend(vd);
bench_unlink_rawfs(rawroot);
section("6. mkdir/rmdir N directories");
bench_mkdir_mem(v);
bench_mkdir_dirbackend(vd);
bench_mkdir_rawfs(rawroot);
section("7. large sequential write/read");
for (size_t i = 0; i < N_LARGE_SIZES; i++) bench_large_mem(v, LARGE_SIZES[i]);
for (size_t i = 0; i < N_LARGE_SIZES; i++) bench_large_rawfs(rawroot, LARGE_SIZES[i], 0);
for (size_t i = 0; i < N_LARGE_SIZES; i++) bench_large_rawfs(rawroot, LARGE_SIZES[i], 1);
/* ---- pack: build one, then random-access read it ---- */
section("8. random-access read: mmap'd pack vs. raw fs");
{
/* re-populate mem with N_SMALL files, then compact into a pack */
for (int i = 0; i < N_SMALL; i++) {
char path[64]; fmt_name(path, sizeof(path), "/f", i);
int err = 0;
VfsFile *f = vfs_open(v, path, VFS_O_WRONLY | VFS_O_CREAT, &err);
vfs_write(f, g_payload, SMALL_SIZE);
vfs_close(f);
}
Backend *ovmem = backend_mem_new();
int oerr = 0;
Vfs *vc = vfs_new();
Backend *ov = backend_overlay_new(pack_path, ovmem, &oerr);
vfs_mount(vc, "/", ov);
for (int i = 0; i < N_SMALL; i++) {
char path[64]; fmt_name(path, sizeof(path), "/f", i);
int err = 0;
VfsFile *f = vfs_open(vc, path, VFS_O_WRONLY | VFS_O_CREAT, &err);
vfs_write(f, g_payload, SMALL_SIZE);
vfs_close(f);
}
double t0 = now_sec();
vfs_sync(vc, "/");
double compact_dt = now_sec() - t0;
record("compact N entries to pack", "pack", compact_dt, N_SMALL, (double)N_SMALL * SMALL_SIZE);
vfs_unmount(vc, "/");
backend_free(ov);
backend_free(ovmem);
vfs_free(vc);
/* same N files as plain files on the raw fs, for the random-read comparison */
for (int i = 0; i < N_SMALL; i++) {
char name[64], path[256];
fmt_name(name, sizeof(name), "/f", i);
snprintf(path, sizeof(path), "%s%s", rawroot, name);
int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
write(fd, g_payload, SMALL_SIZE);
close(fd);
}
int *order = malloc(sizeof(int) * N_SMALL);
srand(12345);
for (int i = 0; i < N_SMALL; i++) order[i] = i;
for (int i = N_SMALL - 1; i > 0; i--) { int j = rand() % (i + 1); int t = order[i]; order[i] = order[j]; order[j] = t; }
Vfs *vp = vfs_new();
int perr = 0;
Backend *ro = backend_pack_new(pack_path, &perr);
vfs_mount(vp, "/", ro);
bench_pack_random(pack_path, order, vp);
bench_rawfs_random(rawroot, order);
vfs_unmount(vp, "/");
backend_free(ro);
vfs_free(vp);
free(order);
}
section("9. concurrency (create+read+unlink)");
bench_concurrency(v, rawroot);
vfs_unmount(v, "/");
backend_free(mem);
vfs_free(v);
vfs_unmount(vd, "/");
backend_free(dir);
vfs_free(vd);
/* cleanup */
char cmd[1200];
snprintf(cmd, sizeof(cmd), "rm -rf '%s' '%s' '%s' '%s.jnl' '%s.tmp'", rawroot, dirroot, pack_path, pack_path, pack_path);
if (system(cmd) != 0) { /* best-effort cleanup; nothing to do if it fails */ }
printf("\n=== summary (%d measurements) ===\n", g_row_count);
printf(" %-28s %-10s %11s %16s %12s\n", "category", "backend", "seconds", "throughput", "MB/s");
for (int i = 0; i < g_row_count; i++) {
Row *r = &g_rows[i];
printf(" %-28s %-10s %10.4fs %14.0f ops/s", r->category, r->backend, r->seconds, r->ops_per_sec);
if (r->mb_per_sec > 0) printf(" %10.1f MB/s", r->mb_per_sec); else printf("%15s", "");
printf("\n");
}
return 0;
}