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perf: cap default tokio worker threads at 16 #11029

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Merged
jdx merged 2 commits into from
Jul 16, 2026
Merged

perf: cap default tokio worker threads at 16 #11029

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5c0ef98
perf: cap default tokio worker threads at 16
jdx Jul 15, 2026
7301b72
style: format tokio worker count expression
jdx Jul 16, 2026
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10 changes: 9 additions & 1 deletion src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -106,7 +106,15 @@ fn main() -> eyre::Result<()> {
let nprocs = std::thread::available_parallelism()
.map(|n| n.get())
.unwrap_or_default();
let threads = crate::env::MISE_JOBS.unwrap_or(nprocs).max(8);
// Tokio spawns every worker thread eagerly when the runtime is built, so
// the default worker count is startup cost paid by every invocation —
// clone + stack + TLS per thread before any work happens. Async I/O
// doesn't need a worker per core (blocking work uses tokio's separate
// on-demand pool), so cap the default on many-core machines. An explicit
// MISE_JOBS still raises it without limit.
let threads = crate::env::MISE_JOBS
.unwrap_or_else(|| nprocs.min(16))
.max(8);
tokio::runtime::Builder::new_multi_thread()
.enable_all()
.worker_threads(threads)
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