less threads

library/std/src/sync/rwlock/tests.rs

@@ -599,7 +599,7 @@ fn test_downgrade_atomic() {
     // itself as no other thread should get in front of it.
 
     // The number of evil writer threads.
-    const W: usize = 1024;
+    const W: usize = if cfg!(miri) { 100 } else { 1000 };
     let rw = Arc::new(RwLock::new(0i32));
 
     // Put the lock in write mode, making all future threads trying to access this go to sleep.