perf: use mimalloc as the runner's global allocator

Cargo.toml

@@ -60,6 +60,7 @@ linux-perf-data = { git = "https://github.com/mstange/linux-perf-data.git", rev
 ] } # unreleased main as of 2026-03-19
 debugid = "0.8.0"
 memmap2 = "0.9.10"
+mimalloc = "0.1"
 nix = { version = "0.31.3", features = ["fs", "time", "user"] }
 futures = "0.3.32"
 runner-shared = { path = "crates/runner-shared" }

src/main.rs

@@ -1,3 +1,9 @@
+// The release binary targets musl, whose allocator is slow on small
+// allocations and serializes threads. Decoding memtrack artifacts allocates per
+// event, which made post-processing take minutes on large artifacts.
+#[global_allocator]
+static GLOBAL: mimalloc::MiMalloc = mimalloc::MiMalloc;
+
 use codspeed_runner::{clean_logger, cli};
 use console::style;
 use log::log_enabled;