chore: fix thread_pool benchmarks (#1947)

Update the rotted thread_pool benchmarks. These benchmarks are not the
greatest, but as of now it is all we have for micro benchmarks.

Adds a little yielding in the parker as it helps a bit.

1 files changed, 9 insertions, 4 deletions

diff --git a/tokio/src/runtime/park.rs b/tokio/src/runtime/park.rs
index 7681e20f..1543bcb1 100644
--- a/tokio/src/runtime/park.rs
+++ b/tokio/src/runtime/park.rs
@@ -4,6 +4,7 @@
 
 use crate::loom::sync::{Arc, Mutex, Condvar};
 use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::thread;
 use crate::park::{Park, Unpark};
 use crate::runtime::time;
 use crate::util::TryLock;
@@ -113,10 +114,14 @@ impl Unpark for Unparker {
 impl Inner {
     /// Park the current thread for at most `dur`.
     fn park(&self) {
-        // If we were previously notified then we consume this notification and
-        // return quickly.
-        if self.state.compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst).is_ok() {
-            return;
+        for _ in 0..3 {
+            // If we were previously notified then we consume this notification and
+            // return quickly.
+            if self.state.compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst).is_ok() {
+                return;
+            }
+
+            thread::yield_now();
         }
 
         if let Some(mut driver) = self.shared.driver.try_lock() {