From 644b445428845a4e662c15059193dfa492bc0c44 Mon Sep 17 00:00:00 2001
From: Stefan Lankes <slankes@eonerc.rwth-aachen.de>
Date: Wed, 24 Nov 2021 15:59:28 +0100
Subject: [PATCH 1/2] If the thread does not get the lock in the short term,
 yield the CPU

Reduces the amount of wasted processor cycles
---
 library/std/src/sys/hermit/mutex.rs | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/library/std/src/sys/hermit/mutex.rs b/library/std/src/sys/hermit/mutex.rs
index 691e7e07902d8..79692ef2442ca 100644
--- a/library/std/src/sys/hermit/mutex.rs
+++ b/library/std/src/sys/hermit/mutex.rs
@@ -46,8 +46,17 @@ impl<T> Spinlock<T> {
     #[inline]
     fn obtain_lock(&self) {
         let ticket = self.queue.fetch_add(1, Ordering::SeqCst) + 1;
+        let mut counter: u16 = 0;
         while self.dequeue.load(Ordering::SeqCst) != ticket {
-            hint::spin_loop();
+            counter = counter + 1;
+            if counter < 100 {
+                hint::spin_loop();
+            } else {
+                counter = 0;
+                unsafe {
+                    abi::yield_now();
+                }
+            }
         }
     }
 

From 6911af9d06ef4f92659326ce426c6aefc7b47282 Mon Sep 17 00:00:00 2001
From: Stefan Lankes <stlankes@users.noreply.github.com>
Date: Wed, 24 Nov 2021 21:12:56 +0100
Subject: [PATCH 2/2] Improving the readability

Co-authored-by: kennytm <kennytm@gmail.com>
---
 library/std/src/sys/hermit/mutex.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/library/std/src/sys/hermit/mutex.rs b/library/std/src/sys/hermit/mutex.rs
index 79692ef2442ca..415cbba101c67 100644
--- a/library/std/src/sys/hermit/mutex.rs
+++ b/library/std/src/sys/hermit/mutex.rs
@@ -48,7 +48,7 @@ impl<T> Spinlock<T> {
         let ticket = self.queue.fetch_add(1, Ordering::SeqCst) + 1;
         let mut counter: u16 = 0;
         while self.dequeue.load(Ordering::SeqCst) != ticket {
-            counter = counter + 1;
+            counter += 1;
             if counter < 100 {
                 hint::spin_loop();
             } else {