55 lines
1.9 KiB
Rust
55 lines
1.9 KiB
Rust
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//! Worker-thread policy for multi-thread tokio runtimes.
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//!
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//! Tokio defaults to one worker per core. On many-core shared hosts (100+-core
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//! HPC login nodes) that pins 100+ thread slots per grok process against
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//! per-user ceilings — systemd user-slice `pids.max` (commonly 1000) or
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//! `RLIMIT_NPROC` — and later thread spawns die with EAGAIN. Grok's runtimes
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//! are I/O-bound, so throughput does not scale with workers past a small
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//! count.
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//!
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//! This is the single home for the cap policy; every multi-thread runtime in
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//! the workspace (the `grok` binary, the `workspace_server` daemon) derives
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//! its worker count from here so the policy cannot drift across crates.
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use std::num::NonZeroUsize;
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/// Maximum runtime worker threads for any grok process.
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pub const MAX_WORKER_THREADS: NonZeroUsize = NonZeroUsize::new(8).unwrap();
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/// Pure, testable: `min(cores, MAX_WORKER_THREADS)`.
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pub fn cap_worker_threads(cores: NonZeroUsize) -> NonZeroUsize {
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cores.min(MAX_WORKER_THREADS)
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}
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/// Reads the host: `min(available_parallelism, MAX_WORKER_THREADS)`.
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pub fn capped_worker_threads() -> NonZeroUsize {
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cap_worker_threads(std::thread::available_parallelism().unwrap_or(NonZeroUsize::MIN))
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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fn nz(n: usize) -> NonZeroUsize {
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NonZeroUsize::new(n).unwrap()
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}
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#[test]
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fn cap_is_identity_at_or_below_max() {
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assert_eq!(cap_worker_threads(nz(1)), nz(1));
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assert_eq!(cap_worker_threads(nz(4)), nz(4));
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assert_eq!(cap_worker_threads(nz(8)), nz(8));
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}
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#[test]
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fn cap_clamps_many_core_hosts() {
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assert_eq!(cap_worker_threads(nz(9)), nz(8));
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assert_eq!(cap_worker_threads(nz(360)), nz(8));
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}
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#[test]
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fn capped_worker_threads_stays_in_bounds() {
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let n = capped_worker_threads();
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assert!(n <= MAX_WORKER_THREADS, "got {n}");
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}
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}
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