Commit 9ff33bbc authored by Chris Wilson's avatar Chris Wilson Committed by Joonas Lahtinen
Browse files

drm/i915: Reduce locking around i915_active_acquire_preallocate_barrier() 



As the conversion between idle-barrier and full i915_active_fence is
already serialised by explicit memory barriers, we can reduce the
spinlock in i915_active_acquire_preallocate_barrier() for finding an
idle-barrier to reuse to an RCU read lock to ensure the fence remains
valid, only taking the spinlock for the update of the rbtree itself.

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarThomas Hellström <thomas.hellstrom@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200731085015.32368-6-chris@chris-wilson.co.uk


Signed-off-by: default avatarRodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: default avatarJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
parent e28860ae

drivers/gpu/drm/i915/i915_active.c

+5 −5
Original line number Diff line number Diff line
@@ -807,7 +807,6 @@ static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx) 
	if (RB_EMPTY_ROOT(&ref->tree))

		return NULL;



	spin_lock_irq(&ref->tree_lock);

	GEM_BUG_ON(i915_active_is_idle(ref));



	/*
@@ -833,9 +832,9 @@ static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx) 


		prev = p;

		if (node->timeline < idx)

			p = p->rb_right;

			p = READ_ONCE(p->rb_right);

		else

			p = p->rb_left;

			p = READ_ONCE(p->rb_left);

	}



	/*
@@ -872,11 +871,10 @@ static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx) 
			goto match;

	}



	spin_unlock_irq(&ref->tree_lock);



	return NULL;



match:

	spin_lock_irq(&ref->tree_lock);

	rb_erase(p, &ref->tree); /* Hide from waits and sibling allocations */

	if (p == &ref->cache->node)

		WRITE_ONCE(ref->cache, NULL);
@@ -910,7 +908,9 @@ int i915_active_acquire_preallocate_barrier(struct i915_active *ref, 
		struct llist_node *prev = first;

		struct active_node *node;



		rcu_read_lock();

		node = reuse_idle_barrier(ref, idx);

		rcu_read_unlock();

		if (!node) {

			node = kmem_cache_alloc(global.slab_cache, GFP_KERNEL);

			if (!node)