locking: rwsem: spin faster

fenrus75 · xdevs23 · commit c40479501109 · 2020-08-04T18:22:28.000+02:00
tweak rwsem owner spinning a bit

Signed-off-by: Simao Gomes Viana &lt;devel@superboring.dev&gt;
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
@@ -717,6 +717,7 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
 	struct task_struct *new, *owner;
 	unsigned long flags, new_flags;
 	enum owner_state state;
+	int i = 0;
 
 	owner = rwsem_owner_flags(sem, &flags);
 	state = rwsem_owner_state(owner, flags, nonspinnable);
@@ -750,7 +751,8 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
 			break;
 		}
 
-		cpu_relax();
+		if (i++ > 1000)
+			cpu_relax();
 	}
 	rcu_read_unlock();
 

Original file line number	Diff line number	Diff line change
`@@ -717,6 +717,7 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)`
`717`	`717`	`struct task_struct new, owner;`
`718`	`718`	`unsigned long flags, new_flags;`
`719`	`719`	`enum owner_state state;`
	`720`	`+ int i = 0;`
`720`	`721`
`721`	`722`	`owner = rwsem_owner_flags(sem, &flags);`
`722`	`723`	`state = rwsem_owner_state(owner, flags, nonspinnable);`
`@@ -750,7 +751,8 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)`
`750`	`751`	`break;`
`751`	`752`	`}`
`752`	`753`
`753`		`- cpu_relax();`
	`754`	`+ if (i++ > 1000)`
	`755`	`+ cpu_relax();`
`754`	`756`	`}`
`755`	`757`	`rcu_read_unlock();`
`756`	`758`