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test(fspy-benchmark): add a contended access row #679

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Merged
wan9chi merged 1 commit into from
Aug 18, 2026
Merged

test(fspy-benchmark): add a contended access row #679

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32 changes: 26 additions & 6 deletions crates/fspy_benchmark/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,10 +29,6 @@ const DYNAMIC_TARGET: &str = env!("CARGO_BIN_FILE_FSPY_BENCHMARK_TARGET");
#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
const STATIC_TARGET: &str = env!("CARGO_BIN_FILE_FSPY_BENCHMARK_STATIC_TARGET");

/// Threads the target runs, passed through to it. Two, because a process that
/// fspy tracks rarely accesses files from one thread.
const THREADS: &str = "2";

/// What a suite reads out of its launches.
#[derive(Clone, Copy)]
enum Metric {
Expand All @@ -44,6 +40,10 @@ enum Metric {

struct Suite {
name: &'static str,
/// Threads the target runs, passed through to it. Two for most suites,
/// because a process that fspy tracks rarely accesses files from one
/// thread.
threads: &'static str,
/// Opens per target thread, passed through to it.
opens: &'static str,
/// Measured iterations. Each one launches every arm once.
Expand All @@ -62,6 +62,7 @@ struct Suite {
/// affords fewer of them in the same time.
const LAUNCH_SUITE: Suite = Suite {
name: "launch",
threads: "2",
opens: "0",
iterations: if cfg!(windows) { 150 } else { 300 },
warmup: 5,
Expand All @@ -75,6 +76,7 @@ const LAUNCH_SUITE: Suite = Suite {
/// joining on top.
const ACCESS_SUITE: Suite = Suite {
name: "access",
threads: "2",
opens: "2048",
iterations: 102,
warmup: 3,
Expand All @@ -84,13 +86,30 @@ const ACCESS_SUITE: Suite = Suite {

const RELATIVE_ACCESS_SUITE: Suite = Suite {
name: "access-relative",
threads: "2",
opens: "2048",
iterations: 102,
warmup: 3,
metric: Metric::Typical,
relative: true,
};

/// The same opens under enough threads to make them fight over the tracker's
/// shared counters. Each record costs two atomic read-modify-writes on words
/// every other thread is also touching, so this is the row that prices how
/// that contention scales; the two-thread rows barely provoke it. Runs half
/// the iterations of the plain suite over half the opens, so four times the
/// threads cost about the same wall clock.
const CONTENDED_ACCESS_SUITE: Suite = Suite {
name: "access-contended",
threads: "8",
opens: "1024",
iterations: 54,
warmup: 3,
metric: Metric::Typical,
relative: false,
};

struct Backend {
name: &'static str,
target: &'static str,
Expand All @@ -114,7 +133,8 @@ fn main() {
validate(base_launcher, backend.target, relative);
}
}
for suite in [&LAUNCH_SUITE, &ACCESS_SUITE, &RELATIVE_ACCESS_SUITE] {
for suite in [&LAUNCH_SUITE, &ACCESS_SUITE, &RELATIVE_ACCESS_SUITE, &CONTENDED_ACCESS_SUITE]
{
run_suite(backend, suite, base_launcher.as_deref());
}
}
Expand Down Expand Up @@ -237,7 +257,7 @@ fn launch(launcher: &OsStr, mode: Option<&str>, backend: &Backend, suite: &Suite
command.arg("--relative");
}
let output = command
.args([backend.target, THREADS, suite.opens])
.args([backend.target, suite.threads, suite.opens])
.stdin(Stdio::null())
.stderr(Stdio::inherit())
.output()
Expand Down
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