On 15/07/2020 12:50, Chris Wilson wrote:
Whenever an i915_active idles, we prune its tree of old fence slots to
prevent a gradual leak should it be used to track many, many timelines.
The downside is that we then have to frequently reallocate the rbtree.
A compromise is that we keep the most recently used fence slot, and
reuse that for the next active reference as that is the most likely
timeline to be reused.
>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_active.c | 27 ++++++++++++++++++++-------
drivers/gpu/drm/i915/i915_active.h | 4 ----
2 files changed, 20 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
index 799282fb1bb9..0854b1552bc1 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -130,8 +130,8 @@ static inline void debug_active_assert(struct i915_active *ref) { }
static void
__active_retire(struct i915_active *ref)
{
+ struct rb_root root = RB_ROOT;
struct active_node *it, *n;
- struct rb_root root;
unsigned long flags;
GEM_BUG_ON(i915_active_is_idle(ref));
@@ -143,9 +143,21 @@ __active_retire(struct i915_active *ref)
GEM_BUG_ON(rcu_access_pointer(ref->excl.fence));
debug_active_deactivate(ref);
- root = ref->tree;
- ref->tree = RB_ROOT;
- ref->cache = NULL;
+ /* Even if we have not used the cache, we may still have a barrier */
+ if (!ref->cache)
+ ref->cache = fetch_node(ref->tree.rb_node);
+
+ /* Keep the MRU cached node for reuse */
+ if (ref->cache) {
+ /* Discard all other nodes in the tree */
+ rb_erase(&ref->cache->node, &ref->tree);
+ root = ref->tree;
+
+ /* Rebuild the tree with only the cached node */
+ rb_link_node(&ref->cache->node, NULL, &ref->tree.rb_node);
+ rb_insert_color(&ref->cache->node, &ref->tree);
+ GEM_BUG_ON(ref->tree.rb_node != &ref->cache->node);
+ }
spin_unlock_irqrestore(&ref->tree_lock, flags);
@@ -156,6 +168,7 @@ __active_retire(struct i915_active *ref)
/* ... except if you wait on it, you must manage your own references! */
wake_up_var(ref);
+ /* Finally free the discarded timeline tree */
rbtree_postorder_for_each_entry_safe(it, n, &root, node) {
GEM_BUG_ON(i915_active_fence_isset(&it->base));
kmem_cache_free(global.slab_cache, it);
Here it frees everything.. so how does ref->cache, being in the tree,
survives?
@@ -750,16 +763,16 @@ int i915_sw_fence_await_active(struct i915_sw_fence *fence,
return await_active(ref, flags, sw_await_fence, fence, fence);
}
-#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
void i915_active_fini(struct i915_active *ref)
{
debug_active_fini(ref);
GEM_BUG_ON(atomic_read(&ref->count));
GEM_BUG_ON(work_pending(&ref->work));
- GEM_BUG_ON(!RB_EMPTY_ROOT(&ref->tree));
mutex_destroy(&ref->mutex);
+
+ if (ref->cache)
+ kmem_cache_free(global.slab_cache, ref->cache);
}
-#endif
static inline bool is_idle_barrier(struct active_node *node, u64 idx)
{
diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
index 73ded3c52a04..b9e0394e2975 100644
--- a/drivers/gpu/drm/i915/i915_active.h
+++ b/drivers/gpu/drm/i915/i915_active.h
@@ -217,11 +217,7 @@ i915_active_is_idle(const struct i915_active *ref)
return !atomic_read(&ref->count);
}
-#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
void i915_active_fini(struct i915_active *ref);
-#else
-static inline void i915_active_fini(struct i915_active *ref) { }
-#endif
int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
struct intel_engine_cs *engine);
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