[PATCH 21/58] drm/i915: Teach the i915_dependency to use a double-lock
Chris Wilson
chris at chris-wilson.co.uk
Wed Jan 6 11:28:07 UTC 2021
Currently, we construct and teardown the i915_dependency chains using a
global spinlock. As the lists are entirely local, it should be possible
to use an double-lock with an explicit nesting [signaler -> waiter,
always] and so avoid the costly convenience of a global spinlock.
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
drivers/gpu/drm/i915/i915_request.c | 2 +-
drivers/gpu/drm/i915/i915_scheduler.c | 65 +++++++++++++--------
drivers/gpu/drm/i915/i915_scheduler.h | 2 +-
drivers/gpu/drm/i915/i915_scheduler_types.h | 2 +
4 files changed, 46 insertions(+), 25 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 5c3b575855f1..600e681e4894 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -330,7 +330,7 @@ bool i915_request_retire(struct i915_request *rq)
intel_context_unpin(rq->context);
free_capture_list(rq);
- i915_sched_node_fini(&rq->sched);
+ i915_sched_node_retire(&rq->sched);
i915_request_put(rq);
return true;
diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
index 264ed53821d8..8391841d927d 100644
--- a/drivers/gpu/drm/i915/i915_scheduler.c
+++ b/drivers/gpu/drm/i915/i915_scheduler.c
@@ -19,6 +19,17 @@ static struct i915_global_scheduler {
static DEFINE_SPINLOCK(schedule_lock);
+static struct i915_sched_node *node_get(struct i915_sched_node *node)
+{
+ i915_request_get(container_of(node, struct i915_request, sched));
+ return node;
+}
+
+static void node_put(struct i915_sched_node *node)
+{
+ i915_request_put(container_of(node, struct i915_request, sched));
+}
+
static const struct i915_request *
node_to_request(const struct i915_sched_node *node)
{
@@ -353,6 +364,8 @@ void i915_request_set_priority(struct i915_request *rq, int prio)
void i915_sched_node_init(struct i915_sched_node *node)
{
+ spin_lock_init(&node->lock);
+
INIT_LIST_HEAD(&node->signalers_list);
INIT_LIST_HEAD(&node->waiters_list);
INIT_LIST_HEAD(&node->link);
@@ -377,10 +390,17 @@ i915_dependency_alloc(void)
return kmem_cache_alloc(global.slab_dependencies, GFP_KERNEL);
}
+static void
+rcu_dependency_free(struct rcu_head *rcu)
+{
+ kmem_cache_free(global.slab_dependencies,
+ container_of(rcu, typeof(struct i915_dependency), rcu));
+}
+
static void
i915_dependency_free(struct i915_dependency *dep)
{
- kmem_cache_free(global.slab_dependencies, dep);
+ call_rcu(&dep->rcu, rcu_dependency_free);
}
bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
@@ -390,24 +410,27 @@ bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
{
bool ret = false;
- spin_lock_irq(&schedule_lock);
+ /* The signal->lock is always the outer lock in this double-lock. */
+ spin_lock(&signal->lock);
if (!node_signaled(signal)) {
INIT_LIST_HEAD(&dep->dfs_link);
dep->signaler = signal;
- dep->waiter = node;
+ dep->waiter = node_get(node);
dep->flags = flags;
/* All set, now publish. Beware the lockless walkers. */
+ spin_lock_nested(&node->lock, SINGLE_DEPTH_NESTING);
list_add_rcu(&dep->signal_link, &node->signalers_list);
list_add_rcu(&dep->wait_link, &signal->waiters_list);
+ spin_unlock(&node->lock);
/* Propagate the chains */
node->flags |= signal->flags;
ret = true;
}
- spin_unlock_irq(&schedule_lock);
+ spin_unlock(&signal->lock);
return ret;
}
@@ -429,39 +452,36 @@ int i915_sched_node_add_dependency(struct i915_sched_node *node,
return 0;
}
-void i915_sched_node_fini(struct i915_sched_node *node)
+void i915_sched_node_retire(struct i915_sched_node *node)
{
struct i915_dependency *dep, *tmp;
- spin_lock_irq(&schedule_lock);
-
/*
* Everyone we depended upon (the fences we wait to be signaled)
* should retire before us and remove themselves from our list.
* However, retirement is run independently on each timeline and
- * so we may be called out-of-order.
+ * so we may be called out-of-order. As we need to avoid taking
+ * the signaler's lock, just mark up our completion and be wary
+ * in traversing the signalers->waiters_list.
*/
- list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
- GEM_BUG_ON(!list_empty(&dep->dfs_link));
-
- list_del_rcu(&dep->wait_link);
- if (dep->flags & I915_DEPENDENCY_ALLOC)
- i915_dependency_free(dep);
- }
- INIT_LIST_HEAD(&node->signalers_list);
/* Remove ourselves from everyone who depends upon us */
+ spin_lock(&node->lock);
list_for_each_entry_safe(dep, tmp, &node->waiters_list, wait_link) {
- GEM_BUG_ON(dep->signaler != node);
- GEM_BUG_ON(!list_empty(&dep->dfs_link));
+ struct i915_sched_node *w = dep->waiter;
+ GEM_BUG_ON(dep->signaler != node);
+
+ spin_lock_nested(&w->lock, SINGLE_DEPTH_NESTING);
list_del_rcu(&dep->signal_link);
+ spin_unlock(&w->lock);
+ node_put(w);
+
if (dep->flags & I915_DEPENDENCY_ALLOC)
i915_dependency_free(dep);
}
- INIT_LIST_HEAD(&node->waiters_list);
-
- spin_unlock_irq(&schedule_lock);
+ INIT_LIST_HEAD_RCU(&node->waiters_list);
+ spin_unlock(&node->lock);
}
void i915_request_show_with_schedule(struct drm_printer *m,
@@ -512,8 +532,7 @@ static struct i915_global_scheduler global = { {
int __init i915_global_scheduler_init(void)
{
global.slab_dependencies = KMEM_CACHE(i915_dependency,
- SLAB_HWCACHE_ALIGN |
- SLAB_TYPESAFE_BY_RCU);
+ SLAB_HWCACHE_ALIGN);
if (!global.slab_dependencies)
return -ENOMEM;
diff --git a/drivers/gpu/drm/i915/i915_scheduler.h b/drivers/gpu/drm/i915/i915_scheduler.h
index ccee506c9a26..a045be784c67 100644
--- a/drivers/gpu/drm/i915/i915_scheduler.h
+++ b/drivers/gpu/drm/i915/i915_scheduler.h
@@ -33,7 +33,7 @@ int i915_sched_node_add_dependency(struct i915_sched_node *node,
struct i915_sched_node *signal,
unsigned long flags);
-void i915_sched_node_fini(struct i915_sched_node *node);
+void i915_sched_node_retire(struct i915_sched_node *node);
void i915_request_set_priority(struct i915_request *request, int prio);
diff --git a/drivers/gpu/drm/i915/i915_scheduler_types.h b/drivers/gpu/drm/i915/i915_scheduler_types.h
index 343ed44d5ed4..623bf41fcf35 100644
--- a/drivers/gpu/drm/i915/i915_scheduler_types.h
+++ b/drivers/gpu/drm/i915/i915_scheduler_types.h
@@ -60,6 +60,7 @@ struct i915_sched_attr {
* others.
*/
struct i915_sched_node {
+ spinlock_t lock; /* protect the lists */
struct list_head signalers_list; /* those before us, we depend upon */
struct list_head waiters_list; /* those after us, they depend upon us */
struct list_head link;
@@ -75,6 +76,7 @@ struct i915_dependency {
struct list_head signal_link;
struct list_head wait_link;
struct list_head dfs_link;
+ struct rcu_head rcu;
unsigned long flags;
#define I915_DEPENDENCY_ALLOC BIT(0)
#define I915_DEPENDENCY_EXTERNAL BIT(1)
--
2.20.1
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