Add benchmark comparing the two variants of allow_threads.

pyo3-benches/benches/bench_gil.rs

@@ -1,4 +1,6 @@
-use codspeed_criterion_compat::{criterion_group, criterion_main, BatchSize, Bencher, Criterion};
+use codspeed_criterion_compat::{
+    black_box, criterion_group, criterion_main, BatchSize, Bencher, Criterion,
+};
 
 use pyo3::{prelude::*, GILPool};
 
@@ -27,10 +29,24 @@ fn bench_dirty_acquire_gil(b: &mut Bencher<'_>) {
     );
 }
 
+fn bench_allow_threads(b: &mut Bencher<'_>) {
+    Python::with_gil(|py| {
+        b.iter(|| py.allow_threads(|| black_box(42)));
+    });
+}
+
+fn bench_unsafe_allow_threads(b: &mut Bencher<'_>) {
+    Python::with_gil(|py| {
+        b.iter(|| unsafe { py.unsafe_allow_threads(|| black_box(42)) });
+    });
+}
+
 fn criterion_benchmark(c: &mut Criterion) {
     c.bench_function("clean_gilpool_new", bench_clean_gilpool_new);
     c.bench_function("clean_acquire_gil", bench_clean_acquire_gil);
     c.bench_function("dirty_acquire_gil", bench_dirty_acquire_gil);
+    c.bench_function("allow_threads", bench_allow_threads);
+    c.bench_function("unsafe_allow_threads", bench_unsafe_allow_threads);
 }
 
 criterion_group!(benches, criterion_benchmark);